Their husbandry is about the same as a ball python. Some things are different, but they are close. I suggest looking up a care sheet on here for them. Most boas I have dealt with (which is not a lot) are docile like most ball pythons too, but like I said, I have a limited experience with them.
I am sure a 55 gallon show or long would work for one, but I always advise against an aquarium for larger snakes. There are some made specially for them with sliding, latching tops that are good, but humidity is hard to maintain in them.
As for price, you can find normal common red tails on Kingsnake.com for around $50-60 plus shipping for babies.