Recently, I purchased the Frisco 52-inch cat tree and I've really enjoyed it so far. So has my kitty. You can find it on Chewy.com for only $40. It's very well made in my opinion and a great tree for the value.
Check out Groupon. They keep putting cat trees up on their site.
I have a huge solid cat tree I bought from Drs Foster Smith for my cats but it's way over your budget.