If you want a D20-based ready-to-use rules system for Cyberpunk games you really need look no further than Etherscope. Okay, its got the victorian element in it, but if you ignore the pictures the cybernaughtics and scope rules work perfectly well for cyberpunk, and the class options are better flavoured to cyberpunk than the more generic ones from D20M or Spycrapt. The scope rules in etherscope also make the traditional Net running a lot more available to all characters, and therefore prevents the usual split party issues you get when running a cyberpunk scenario where the net runner is the only one able to enter the net.
If you're looking for a setting, Etherscope isn't a standard cyberpunk setting, but it is true to cyberpunk themes and if you fancy cyberpunk "with a twist" Etherscope is,in my (obviously biased) opinion, but also in the opinion of many reviewers, much better at keeping to the true themes of cyberpunk than Shadowrun. If on the other hand you're looking for a system to pick up and run for your own homebrew setting, I think you'll find Etherscope a lot closer to what your after than OGL Cybernet (which I find devoid of flavour) and D20 Cyberspace (which requires a bit of work to sort out what you want from what you don't, and doesn't do the cool Matrix-style net combat that Etherscope does). Plus Etherscope's second printing rulebook is available at a reduced price, I think (Fanboy 3 in Manchester had it for £9.99, so about $15ish?)
Cheerio,
Ben