I am upgrading my hp p7-1234 with a graphics card, and I need to know what the best graphics card that is compatible with my pc and at a price of 100-200$
(I see no better solution at all. A half decent R9-270X is at least $180 which requires at least a $40 power supply so that's almost double the cost for about 35% more processing power. Also, you wouldn't get 35% more on average with that AMD CPU since it would bottleneck compared to the INTEL the tests were run on for the benchmark. Perhaps 20% at best on average depending on the games chosen.)
I'm going to go ahead and suggest an nVidia GTX 750 Ti as your best option without having to replace the power supply, and the card is fairly easily available in your price range.
(I see no better solution at all. A half decent R9-270X is at least $180 which requires at least a $40 power supply so that's almost double the cost for about 35% more processing power. Also, you wouldn't get 35% more on average with that AMD CPU since it would bottleneck compared to the INTEL the tests were run on for the benchmark. Perhaps 20% at best on average depending on the games chosen.)