A GeForce FX 5200 isn't worth $50.

They'd probably give you $15, if anything.
I'm not a big fan of flashing the BIOS of videocards, so that's up to you. I know it's possible on a lot of videocards, particularly the GeForce FX 5900 series. I think it's simply better to spend the money and get a card that'll always work without worrying about fucking it up.
Don't buy the Radeon 9800SE...those are shitcans. Get the Pro at least. The regular 9800's aren't that great either. The GeForce FX 5900 is a really nice card though.
-Lasereth