Following through on my "Boa Fever" I've decided to take the leap and start off with a Colombian Boa constrictor...for now

I'm looking at getting a male, so anywhere from 5-7ft. So far, Animal Plastics has the least confusing website to cruise myself through. Would a T8 be fine or should I jump on the T10?
I don't have money to spend all willy-nilly unfortunately (besides random vet visits, food, and other cares and necessities), so this would be the final cage. Would I need bigger? Any other brands recommended that won't cost me all my limbs?
Any advice appreciated