Typical new price in the UK is now about £170 (approx $320). Second hand prices fluctuate a lot but most dealers are asking the same for used ones!
I'd buy another if I could get it for $75 but certainly not $250
There is certainly is still a market for 780s, but the price is going to continue to drop as more 785s and even 796s hit the market. $75.00 is definitely at the lowest end of the scale, but I think $250.00 is at the highest end.
As more systems go digital and with 800 rebanding looming, the market for 780s will continue to shrink.
since the 785 can't trunk track any motorola systems that are rebanded the price of them will fall rapidly in the future. This will result in the 780 dropping drasticly. If you can sell one for a good price now is the time to do it. If your buying one, realize that it will have limited value in the future.