Thanks again for the replies... I've been away to a conference the last three days, so haven't had time to check the forums.
Well, my $30 tree arrived today... I was somewhat skeptical, as I went to petsmart before it arrived and saw the ~ $130 - $170 trees there (of similar size to the one I got) that were quite unstable...
So, I get home to find a BIG box. It was easy to assemble (30 min at most). I was pleasently surprised by the size of the cat cubby on the bottom of the tree... The first and second levels are pretty sturdy, even if the 2nd and top are a little on the small side. The top level isn't very sturdy. The undersides of the shelves are also not carpeted (oh well). And, for anyone possibly interested in this tree, the tunnel is NOT big enough for a cat to get in (kitten maybe) but it will hold toys, etc.
The cat's weren't too keen on it at first, but then, with a little catnip and some toys, they climbed all over it. (although still not so keen on the top level).
The other folks in the house think it's hidious (and, I must admit it is very much a classic carpeted cat tree, so not the height of home decor), so it will be staying in my room for now.
It is also oddly shaped (with the two top levels being uneven with the bottom cubby) so putting it right in a corner (with wall contact to stabalize it on the bottom or top shelves) isn't an option. So, for now, it's in front of one of my windows.
Now, although it IS hidious, I must say that I enjoy watching the cats climb on it and, for a brief moment, I was considering getting on ebay and going for a larger/sturdier tree. But I think I'll have to wait until I have more space. Although I might get a corner-specific unit for the originally inteded place.
So, now I can begin putting a little money away for the LR and/or a better tree.
Thank you all for your help and if anyone has any more suggustions on cat trees, etc. I'd be more than happy to hear them! I'm still intersted in getting a "corner unit" so if anyone has any feedback on those models, please let me know.