What is a cheap graphics card for my HP Pavilion desktop computer?

I have a 4GB Memory RAM, 64- Bit operating system, Pentium (R) Dual-Core CPU with 2.50 GHZ. Also, would i need a video card? It is for the game Skyrim on Steam/|||nVidia GeForce GTX460, 1024MB, GDDR5 -> has a good price for what it can do.