Doesn't work that way. PC gaming is expensive, the end. You're constantly upgrading SOMETHING. Video card, RAM, CPU, HDD. It's a never ending treadmill. The only real inexpensive gaming computers out there are called consoles. You buy one bit of hardware, and that's typically good for 3-5 years, though lately it seems to have been extended to more like 5-7 years with Microsoft and Sony both breaking the bank to add raw power.
If you do get a PC for gaming, make sure it is NOT a laptop. Laptops are HORRIBLE gaming systems. Smaller, lower resolution screens with higher response rates, lower end mobile graphics and CPU, virtually no upgrade path, and what you are able to upgrade costs more. Not to mention gaming causes the system to work harder, meaning more heat is generated, and with laptops, there's not as much space for that heat to go, so it just tends to sit there, slowly baking the internal components.
I will also say, while it's far from cheap, Apple's Mac Pro could make for a decent gaming system. The 8 or 12 core models in particular. I'm not sure if the ATI cards can be configured in some kind of SLI setup or not, and the ECC RAM is slightly slower than non-ECC RAM, the RAM part would almost certainly be made up for by having dual quad or six core CPUs, complete with hyperthreading to create 16 or 34 virtual cores, and the RAM is physically located on the same little removable tray as the CPUs, so the distance the data has to travel is virtually zero, which should help make up for some of the latency caused by the extra error checking bit on the ECC RAM. Of course the 8-core model starts at about $3500, so not exactly cheap by most people's standards.
I'm a convinced Apple fan, but would like to get back into the world of gaming. I was thinking about a second computer (laptop or desktop) for just that purpose. Can anyone help me out with the sorts of requirements a gaming computer has, and what it doesn't need to have? Also, of course, staying as inexpensive as possible.