I dont know which country you are in so i cant really tell you how much 
However, those specs are found in computers several years old. I have a dell optiplex 780 that i bought on ebay a couple of years ago for £100 and I put in a nvidia graphics card for £30. It has a 3GHz processor(DC), 4GB RAM.
Basically, any cheap computer made in the last 5 years should do it, you just might have to replaced the graphics card for a better one. Any with onboard graphics is likely to be kak