While my box is nothing to sneeze at, it certainly isn't the latest and greatest. CS look pretty good to me (except when there's water in the map, then my framerate goes to about 15fps).
I've found that you can usually upgrade an existing system for a couple of hundred bucks. I always go to ArsTechnica and look at their
budget box specs. You just need a new Motherboard, memory, processor and video card. $401.68 from their web page. You can reuse the rest of your computer parts. Now if you aren't computer savy, I'm sure you know someone who is. Just buy them some beer and hand them the parts and your computer. Don't hand them the beer until you get the computer back and it works. I've not owned a brand new computer in years. I just keep swapping out parts in the old one. Eventually you've got a completely different computer, but you always have something relatively up to date.