I have been mountain biking for over 20 years. For me it was a very simple decision. I found the first bike that was totally awesome. It was the best. But I'm dedicated to dirt. I'm 135 pounds.
Having said that, it shouldn't be any different finding a bike for you. I can send you to a forum where you can get the answers.
There are so many ways to go. Last night I just decided to peruse all of the separate bike forums to look at all of the different bikes. I was amazed at what is out there. From Surly, with huge fatty tires, to Moots with the titanium suspension. Or even the single speed bikes. The single speeds are totally pared down and light. I get such a thrill seeing all of the really well made bikes. And the posts of the people who, like us, ride them. I saw a guy with a trailer riding through Australia. In the middle of nowhere.
Your size isn't a problem. The Clydesdale forum has a post right now for a guy who's seven feet tall.
There are two basic bike categories. The mass produced, and the beautiful gems. Basically that translates to Taiwan or USA. But considering the USA frames can be well over your price, alone, that is probably out.
I would suggest full suspension. It's just way more forgiving. Plus, I find that having a cool piece of machinery adds to my desire to go out and play.
To be honest, I would have to do some research to find what the killer deal is right now. Give it some time. I'll keep my eyes open for bike packages in that price. I know it's possible. I have a friend who recently bought a bike for under that price that is supposed to be very nice. And he's Gary Fisher's first employee, with a lot of biking experience. I can ask him.
Mountain bike review is the forum to go to. I've been hanging out there since before 2000.
Here's their product review page-
http://www.mtbr.com/reviews/Here's the general forum page- I suggest doing what I did last night. Scroll down to the individual bike makes, and search through the posts with pictures. Maybe that won't tell you much. I suppose the review page with pricing might be more informative. But if you like bikes, the "show us your bike" posts are pretty fun.
http://forums.mtbr.com/Super ninja edit-
OK, here's a full suspension XC (cross country) mountain bike review listing. If it works, I've got it in descending order of price. Check out the Haro xls r5. Not a bad bike for the price. Wee. Fun! I love searching for cool stuff. More, later...
By the way, each bike listed, has all of the individual reviews under it. Click away and see each bike and what people have to say.
http://www.mtbr.com/reviews/xc_full_suspension/index_byprice.shtml