A few years ago I was getting pretty big into downhill biking, I was riding with a few guys who were ranked nationally in the top 10. Where are you thinking of doing most of your riding? Are you thinking of doing any competitions? We have some incredible downhill trails here in Utah. When I first got started I rode a stock Specialized Enduro, I still love the feel of that bike. I then upgraded to a K2 with a dual crown fork, since then I have experimented on many bikes Kona stinky, stinky deluxe, coiler, Giant DH, Specialized Big Hit, and an Ellsworth Dare.
Check out mtbr.com they have reviews on just about everything bike oriented. And is actually where I buy a lot of my bike components, check out the classifieds. I looked for about a month before I found my never been ridden Specialized Enduro for over half off the sticker price shipped to my door.
There are a lot of reputable brands for downhill bikes, I personally like the bang for the buck that you get with many of the kona rides. I think it is possible for you to find a "decent" beginners downhill bike for less than 1K. Let us know what you are thinking as far as where you will be riding and how much you will use it, then we may be able to help more in steering you in a good direction. Those two bikes that Tacoma suggested were two of the three that I found on ksl that I was going to suggest. The other is a Kona stinky.
On a side note have you or anyone ridden the bobsled this year? I was up there 2 weeks ago, it has changed a lot in the last year, it is a blast now!