All the articles online that I've read say 10 gallons minimum, should I believe that? I'm still researching and saving money for all the supplies, but yet I want to save as much money as possible.
Some people say you can do 10 gallon or 12x12x18. Personally, I have a crested gecko that is an adult now, and it feels too small for her to spend her whole life in it. I'm going to be upgrading her to a 18x18x24 instead.
Unfortunately, there aren't really a lot of nice tanks available that are also inexpensive. Most people save up for the front-opening tanks that run about $100.
If that's really out of reach, you could explore something Do-It-Yourself, like converting a standard tank to an upright or using tubs of some sort. I haven't done any of that though, so you'd have to search for how-tos online.