PVC cages are not like tanks and are much easier to clean and maintain than a tank. This is really the only acceptable type of enclosure for the average adult boa. BABIES can easily be kept in tubs. I have all my babies in a standard 41qt rack. They are moved to 4x2x2 cages at around 2yrs old though. If you do not want to deal with the appropriate cage, perhaps a different type of snake would be better suited for you. But really, they are easy to clean - every bit as easy as a tub! Give it a try - you won't be sorry! And you'll love having a boa!
If you're on a budget and you don't have the snake yet, get the setup first. Keep an eye on CL, local FB forums, etc. for people selling the larger enclosures. Last weekend I picked up two used 32"x18"x8' monster enclosures with a removable center divider, heat, t-stat, and extra doors for $700 - these retail new for $575 each before shipping and accessories.