i buy for a couple of salvage yards and depending on the pieces i find for them i get between 250 and 500 just for locating them and making a deal the salvage yards do the rest (which is mainly newer tractors that aren't many broke yet)
I could see paying $50 or maybe even $100 but there is no way I would pay someone that kind of money just to find one, unless it were an extremely rare tractor. In the case of the tractor I will be looking for (Massey 135 or 150), it's anything but rare.