All I can do is compare it to what I spent and the condition it is in now. It's going to need floorboard patches, rockers, and probably fender patches too. The tailgate looks a little buggered up and has some rust. the rubber is no doubt dry and needing some replacement. The driprails are rusty, but I can't tell how rusty...if it's surface, that's fine, but if it's through, that's more metal work. Springs are flat, so suspension would be good. But hey, on the good side, LOOK AT THOSE WHEELS! BLING!
I don't think I'd pay $4K. But, I also think that it is a super cool truck and I don't know how soon it would be that your would find something "better."
By the way, I have and FJCruiser and a 55 and did the same thing you are considering. Bought the 55 2 years ago and just finished it up in the last week or so.