Maybe $80 for the video card. While the 7900GTX was fast in its day, its day is gone. Looking at toms charts, its hard to see where the 7900GTX fits in these days. At 16x12, it seems to be faster then many cards, but in some games it comes up short. In Oblivion for example, its barely faster then a 2600XT, which is a sub $100 card. The 3850 is faster then it all the time, and that is around $120.
The 2140 currently sells for $75 on newegg. Assuming you are including the heatsink, I would think ~$50 would be a good price.