Pentium 133 MHz, 24 MB RAM, and 400 MB hard-disk space.
So as you see you doesn't need a realy progaming machine to play this game, even a pc like this one or this one   (just joiking for the second one).
 So lets see how mutch you need ($) to play cs.
To start a steam acount with cs costs 9,99€.
Then you must to have a pc .
 A pentium II is realy enough to play cs, on eBayyou can find one for less than 50€.
 For good hed set, keyboard & mous you need a maximum 30€(New) and maybe less on ebay.
 And for your monitor you can find one for free from one of your friends  .
  So all you need is a total of less than 100€ to play cs.
 
  Ofcause your game quiliti will not be realy nice (+/- 20 fps) and a realy long loading is some of the bad things but a lot of people playing with bad pc. I'm steel playing with my (30-60 fps) since three years and it doesen't realy botrhers me.