I keep my 2 larger females (15lb adult, 6lb juvie) in 4' cages from RBI, with aspen bedding, and a water dish. They use Ultratherm heat pads and I have them hooked up to a Helix thermostat, they also have temp/humidity gauges in the cages (the kind from Lowes/Home Depot that everyone talks about up on the BP section of the forum).

As far as cages go, if you want to display I would suggest a nice display cage from RBI, Animal Plastics, Boaphile, ect.. I've used tubs and they are very cheap, but I don't feel they're very good if you want the boa to be a display animal, also, you would have to hook up your own heat tape and drill your own ventilation holes.. I've also used terrariums before, which cost about half as much as the RBI cages I use, but its the biggest pain to keep temps. and humidity correct in them, the only snakes I keep in terrariums now are snakes with low humidity requirements.

I would suggest saving up money to buy a nice display cage/heating pad or tape/thermostat so that the snake has everything it needs.. and IMO shelling out the extra money for a nice cage in the beginning is worth it.