I would point you in the direction of Anandtech. His value gaming system that he did an article on last week is probably the best place to start. He ended up with a really great system including 4.1 sound 19" monitor and decent video for about 750 bucks as I remember. You could probably shave another 200 bucks if you were willing to give a bit on the monitor and speakers. The components he's spec'd out are an excellent place to start. You can find just about all of them on
www.newegg.com. Go look at the article - it should still be on the front page of this site.
Be a bit wary of barebones systems. Unless you look at every little component (and know what the heck you are looking for) you'll probably end up getting what you pay for which is not much.
The two hardest parts of building a PC are: 1) Knowing what components to buy that will work well together and 2) connecting those silly little connectors from the case lights and switches to the motherboard.
Anand has done the first part for you. The second part...hehe that's the adventure (rest assured you can't really burn anything out by screwing it up at least)
Oh yeah... To answer your original question, yes AMD is generally less expensive. Don't confuse this with being "cheap". AMD still performs very well.