Ashish is right but if you plan on playing any modern games a cheap GPU really won't give you a playable FPS. My advice would be don't buy a $100 GPU, save up and get a good one for around $200 like a 7870 Myst or 7870 XT. At the moment they are the best price/performance GPU in my opinion. By doubling the money you spend you wil see 3 or 4 times the FPS and getting a lot longer life out of the $200 GPU.
That should be fine.
Don't worry though; it your budget only allows for a $90 card, the HD7750 will play, just on lowered (perhaps to "medium" on the most demanding titles) settings. If you've read reviews and seen screenshots of current games, you know that medium doesn't exactly suck any more.