Where to buy glass enclosures cheap

Keep an eye on PETCO, and they will periodically hold a "Dollar-a-Gallon" sale on aquariums up to 75 gallons capacity. Not open-front, but unless you find someone selling a used enclosure, you'd probably have to do it yourself.

I have, on occasion seen florists' coolers and wine coolers for sale...

 

Does it need to be glass?
I've found the ExoTerra rarely drop much in price. The cheapest prices you'll find are usually at reptile shows, but the XL will still run ~$300. I occasionally see cheaper ones used - best bet for those is Facebook Marketplace or joining a Facebook group of local frog/terrarium people.

If you are okay not using glass, I'm a big fan of the smallest VivoSun tents. They've got a variety of smaller sizes - I've got a couple of the 30" x 18" x 36". Those are generally less than $100, and you could probably find a gray market brand for even less.

To echo what Ray said, you can also sometimes find wine coolers for less than $100 (or about that price). Again, Facebook Marketplace is a great stop for them. I found a scratch/dent store near me that had a bunch of wine coolers available for really cheap. Some were a bit banged up, but all working.

 

Gotcha! Definitely check out Facebook Marketplace.

As for the VivoSun, they’re nice. The lights have to go into the tent though, so you’d want a pretty cool running LED to keep the temp down.

 

You may have some luck on Craigslist. People will sometimes sell old aquariums at quite low prices, if you'll come and haul it away for them. Might need a good scrubbing, though.