I got my cat tree on eBay a few years back. There are some amazing ones on there for really good prices -- and many of them don't charge for shipping. (As always on eBay, check out the seller's feedback. I never buy from anyone with less than 99.5% positives, and I read whatever negative feedback there is to find out what the buyer's issue was.)

Here are my kitties hanging out in theirs:


It stands about 5' high. When the monster tuxedo cat jumps onto that top shelf, the whole unit rocks back and forth for a bit, but no matter how hard they play on it, it has never come close to falling over.