Housing, feeding, cleaning and general maintenance of an adult boa is a lot more exspensive and effort than it is for a ball python. That being said IMO it is worth it x100. In the past 20 years I've kept more species than I care to count from garter snakes to retics to gaboon vipers, and most things in between. I'm not sure I'd ever be able to pick a favorite species. But if I made a top 10 list boas would be on it. They exhibit some of the most amazing personalities of all species I've had the pleasure to work with over the years. Do yourself a favor. Spend the money. Buy a good quality PVC cage. Get yourself a boa, what ever boa that peaks your interest, since their are so many amazing options to choose from these days. You won't be sorry.
If I had a dollar for every ball python keeper just on this forum that gets a boa and is blown away and excited about how much more interesting captives they make than their bp's.....
... Well I'd probably be able to afford a couple more boas lol.