You probably won't get your MIR back half the time, so don't rely on MIRs. Just get a 4850 - it's a good card. It may old, but it outperforms the 4770, equals the GTS250 and costs less than the GTS250.
You can get a used 4850 for ~$80
If you want to go the Nvidia route, go for the GTS250 and hope the rebate company doesn't suck.