My main computer is a desktop that I put together myself with economy parts about two to three years ago. Even then, the parts were somewhat dated - hence the discounted price. Of my original set up, the most expensive component was the hard drive, a 640GB one at $79. The Pentium Dual-Core 2.0 Ghz processor was $69, and the Asus motherboard was an open-box special at $75. The total cost for the computer itself (I'd already picked up a 24" monitor that I'd been using with my laptop at the time) was less than $500. Today, with a subsequent upgrade to a 128GB SSD, a Radeon 5600HD, and having overclocked the CPU to a stable and relatively cool 2.8 Ghz, my budget build handles everything I can throw at it, from large illustration files in Photoshop to The Elder Scrolls: Skyrim . . . all the while powering three screens.
Needless to say, for my first foray into assemble-it-yourself computing, I'm very satisfied. The key to my success in building my own rig wasn't my personal knowledge of the hardware I choose (I had none) or extensive experience with computer assembly (beyond a good intuitive grasp of how things work, there was no experience to speak of). No, I managed to succeed in the sometimes difficult realm of self assembly by relying on the advice of experts and knowing where to source information and user experiences I could count on.
For the basic framework of my rig, I looked to an About.com article on building your own budget PC. As the featured components, I knew that they had to be extremely compatible with one another and a good benchmark for ideal performance levels. I then searched for various computer forums - Overclocked.net being one of them - with sections and members who make a hobby of building their own rigs, and searched for posts about the components in question, or other similar components that I'd considered as substitutes. (Case in point: the Pentium Dual-Core I choose was older, slower, and cheaper than the Core Duo processor the About.com author suggested, but I chose it because of its sterling reputation as an overclock-friendly CPU. As my own machine's 2.8 Ghz operating speed attests, that reputation is well-earned.)
There's a certain amount of risk inherent to building your own rig. There's no customer support safety net if one of your components doesn't work well with the others, beyond its original manufacturer's warranty or the return policy of your vendor. But if you do your homework and purchase from vendors with a good return policy, you can get a system that meets or exceeds your own personal needs at a fraction of the cost of what it might cost you to go the prebuilt route.