well, heres my two cents worth. The question is what is this truck worth to YOU? It really doesnt matter what me, or anyone else for that matter, would pay. How bad do you want it in a market where the price of trucks is on the rise quickly. The fact of the matter is that you are in texas and i considered selling my truck and could have gotten 6k or better any day of the week and i never expected it to go for that high. These were offers that were given to me in person, so you are actually on a fairly decent deal. I simply chose to keep mine, i just couldnt part with it. People want these trucks and they are drying up. Now, having said that imo, you have a decent truck on your hands for anywhere in the ballpark of what you're talking about giving for it. 3000 to 4500 is not a bad price. The trucks biggest enemy right now appears to be rust. It appears that as far as the engine is concerned, the biggest rust spot is the oil canisters. These should be the first thing that goes in the trash for a set of spin ons anyway so this is a moot point. That will eliminate that problem. I would then attack that truck with phosphoric acid to remove the rust and then hit it with the paint of your choice. PROBLEM SOLVED! I would also ask if you could be allowed to remove the instrument cluster and look at the area under the cowling to insure that it has not rusted through. This area seems to be a very nasty point of damage that goes un-noticed. If you find that there is no damage in this area, i would then move on to the rear section of the cab, in the area behind the seats to see if there is any damage there. If you find that this trucks cab is relatively free of severe rust damage, i would jump on it. Replacing a rusted out cab is a huge job that you dont want to tackle if you dont have to. I did also notice that your driver side door is rusted out at the bottom. This is also another place you will have to fix. These are all areas i would point out to drive the price down on your initial offer. The upper radiator hose is an easy fix but while you're there you might as well attack the whole cooling system. Flush the cooling system thoroughly, Remove and inspect the radiator, replace all the hoses from the water pump. Replace the lower radiator hose, then replace the coolant. This is maintenance that should be done upon purchasing a truck any way. You would be amazed at what you will get out of that cooling system. You should also budget in a fresh oil change. I would feel confident in driving the truck routinely after the above is all complete.
I know its long winded but i hope this helps you learn from mistakes that i made.
best of luck