Keep an eye out on your local craigslist, I've seen aquariums of significant size go for a couple hundred. They devalue after use, nobody can get back what they paid for them. I used to grow in an 150 gallon (tall, not wide) tank that could handle the height of flowering vines and mature plants. Even something like that would suit you possibly permanently if you didn't expand your collection too much more, and were willing to cut down vines that got too tall after a while.

For the mean time...square pots! I underestimated how much more space I could make, (and how many more plants I could fit) in my growing area and am now switching everything over slowly. I've been using Hydrofarm square white pots, once I saw them at a local hydroponics store. They're great because they're taller than wide....even more space!