I know you said you aren't a computer genius, but building your own computer is actually very easy. This game requires so little, the computer could cost less than $400, however, i don't know if you are including a monitor in this. Anyway, here is a cut as what you could get. I made it an AMD system as you can go cheap now, and you can upgrade to a better processor/ram later. The processor and video card I am recommending is better than I have now, and Sins runs great for me. You'll need a copy of Windows, your own Keyboard and Mouse, and a Monitor. If you want that, you can buy it on this site as well.
Antec Case - http://www.newegg.com/Product/Product.aspx?Item=N82E16811129033 - $100
Motherboard - http://www.newegg.com/Product/Product.aspx?Item=N82E16813138105 - $58
AMD 3.1Ghz dual core CPU - http://www.newegg.com/Product/Product.aspx?Item=N82E16819103272 - $73
4Gb Ram - http://www.newegg.com/Product/Product.aspx?Item=N82E16820208353 - $34
ATI HD 4830 Video Card - http://www.newegg.com/Product/Product.aspx?Item=N82E16814102803 - $100
DVD Burner - http://www.newegg.com/Product/Product.aspx?Item=N82E16827151179 - $23
640 Gb WD Hard Drive - http://www.newegg.com/Product/Product.aspx?Item=N82E16822136218 - $70
TOTAL ------------------------------------------------------------------> $458 plus about $25 in shipping
EDIT: Wow, I didn't know I could build such nice computer so cheap. If you want to upgrade any of the parts, PM me.