Clint, I'm interested to know why you see it costing so much? Because of the hydraulic system?
Ok, so here's how I get there:
I don't know when M108 production stopped, somewhere in the 1950's. So let's call it 1955 for conversations sake. It's 2015 now, so this is a 60 year old truck.
The OP stated it hasn't run in at least 8 years and that it obviously has a lot of deferred maintenance and that's in addition to it's half-century+ age.
So this is what I would expect to find and what I'd expect to do:
Brakes:
I've had 2 1950's deuces blow the front-to-rear brakeline out on me, rusted from the inside out. I replace all the steel brake lines on all the 1960's cars I work on, so I would definitely plan on having to do these. You can have a local brake line shop (there's one here in Atlanta that's quoted me) for about $35-$30 a line. That includes the spiral armor and saves you the time of bending and flaring. Or you can buy bulk brake line and bend and flare it all yourself. So figure something like $50-$200 for brake lines. Then another $150-$250 for brake hoses, depending upon if you want rubber or stainless. Then an airpack rebuild at $200ish (kit) or an NOS/new one for $500. Then a master cylinder for $55 and at least a gallon or so of fluid ($75 if you're lucky). I'll give that it probably doesn't need shoes but you'd be an idiot to build an all new brake system and not do wheel cylinders. Napa's cost on new and correct units is $204 for 6 of them. Yeah, you can rebuild them for like $100 but all new stuff that's correct (has the right expanders) is a no-brainer. So just on the brake system and this assumes good drums and shoes, you've spent $750ish - $1300. Don't forget the electric mico-lock that's 60+ years old and it likely bad.
Then, since you're doing all the brakes, let's go ahead and do axle boots, inner seals, axle seals, etc. What all is that? $300ish?
Since we're doing all the axles, we might as well burn through a 5 gallon bucket of GL1 and do all the gearboxes with fresh, since there's no guarantee the gear oil isn't ancient, could have water/mud/whatever in it, etc. Can't find the part # to look it up. What's a 5 gallon bucket cost now?
So now we've more or less dealt with the underside and it'll theoretically roll and stop.
Now, get to the running part.
It's a 60 year old gasoline powered vehicle, so figure replacing the gas tank or having it vatted to get the varnish out (my local radiator shop charges like $200-$300 for deuce sized fuel tanks), cleaning or replacing all the fuel lines, replacing or rebuilding the fuel pump, rebuilding the carburetor, etc. So on the low side, figure maybe $200 for the fuel system, up to maybe a thousand, if you get all fancy with an NOS tank, NOS carb, etc.
Then the ignition. Rebuild the distributor with new bushings so the dwell will be halfway accurate, then points, condensor, rotor, cap, etc. Then new waterproof wires ($200? haven't priced OA331 wires but M37 wires are like $200), waterproof plugs (can't remember, $5 each?), etc. If you want a new waterproof 24V coil, you have to buy an NOS one because the repros are bigger trash than the M-series flasher relays. So what have we spent here? $350-$600?
The you figure all new belts and hoses. Let's call that $100.
At a minimum, flush the radiator. That's $10 if you do it at home. If you have to have it recored.................................... get ready to bend over. I've never seen an NOS gasser radiator, so you'll be recoring it and my shop that I've used for 20 years and had good luck with said it would be an $800-$2000 job to do a multi radiator because it's oddball core is expensive. Who knows what a gasser would be.
Then there's all the electrical. You can figure you'll put a few bulbs in it here and there, so let's call this $50.
Oil and fuel filters, plus engine oil change? Guessing here, $150 for everything?
Now, we've got it running and driving, and all on assumptions about EVERYTHING being good: no bad clutches, no worn out trannies, no bad transfer popping out of high range, no low oil pressure or death sounds from the engine, etc. And what have we spent?
Now, it's pointless to own something like and not be able to pick stuff up, so let's go the back.
I don't have to see anything more than those rear pictures to know that wire rope on the boom is toast. Rusty, kinked and broken. I have no idea what a 108 takes on the boom, but if it's 100' of 1/2", then cheapest I can buy that is $360 (for the correct stuff, I am sure incorrect wire is available cheaper), plus the terminals to terminate it (I know the 108 uses that old school ficture that's visible in the pictures, not real familiar with it like I am the esmet front connector).
Now, these beds take some odball hydraulic connectors, to the point that people have had to machine adapters to get modern connectors to attach to the bed. I am sure Recovry4x4 can chip in here and explain in more detail, but the adapters only handle the adapting part of the equation. I think to re-hose a wrecker, whether it's 108 or 816, whatever, is probably $2500. Ask Stretch about hoses-they're all so old that as soon as you start using it, you just replace one hose after another, so when the thing holds... what, 50-80 gallons, it doesn't make sense to do the hoses one at a time, as they blow. Just do them all now.
So $2500 plus 50-80 gallons of hydraulic fluid. And I'm not counting in this estimate having the cylinder(s) repacked, which trust me, you'll be doing soon enough on a truck like this. If I bought a 108, I'd do the cylinders at the same time as the hoses.
So now, we have a truck that theoretically runs, drives, stops, lifts, rotates, etc. And we've invested $4995-$6660 on just the stuff that we know, without even looking at the truck, that it needs. I don't have to see this truck to be 90% sure it needs all this. Sure, maybe somebody put new brake hoses on it in 2005, but now they're 10 years old and starting to dry rot.
And- at my current estimate, I haven't touched any of the following issues:
Tires-you know as old as they are, they're dry rotted. You know it. Sure, you might could get away with them only bombing around town with it, but driving it any distance or using it for work on the road in any way probably means 10 or 11 tires.
Parking brake-you know the shoes are worn, the cable is frozen up, missing a couple of springs, etc. Like they all are.
Windshield wiper blades.
Windshields, window regulators, door latches. At least a few of these are no good.
No seat belts (likely).
Probably has a worn out steering box.
Probably has some wiring issues, with all the wiring being 60+ years old. So new wiring, douglas connectors, etc.
Who wants to take wagers it needs pinion bearings on the middle axle?
And, for all the money that I've hypothetically spent above, I have not assigned a single penny to labor, because all home enthusiasts (myself included) attribute no labor costs to this stuff. So for all the above work, what are we talking---- 200 hours? 200 hours you had to take away from cleaning out the gutters, helping your wife with that exercise pole she wanted in the basement gym, sharpening the lawnmower blades, taking the kid of karate class, going out drinking with your friends, playing GTAV, surfing SS, whatever.