The cost is what made me give up on the idea.
I did find a used on on the east coast for half that.
I know where there are several rolloff truck in a wreking yard here in California. They want 2500 for the setup but it is an unusual slide on top design. It could probably be modified to the standard setup.
If you just want to swap the bed check out swaploader for some ideas.
One idea would be to convert your truck to a dump and add a winch to the front of the bed and a roller to the back.
or just build a small rolloff.
On dump trucks the bed is uually power up and gravity down.
On a roll off the bed is power up and power down. this helps in keeping the loading angle down.
Also the sheeve roll offs usually have more power than the winch models, but the frame has to be thicker to house the rams.
I would not worry about them being top heavy. I used to haul a lot of stump boxes on my rolloff and would commonly scale at 10,000 lbs over weight (60,000 lbs) this was hard on the tires but did not make the truck seam top heavy but then again I had no srings and just a walking beam in the rear. I did love those air lockers.
Personally I prefer the roll off to a hook lift but i am biased based on my experiance.