Here is a Pro-Line 4' X 2' X 14". it was $263 delivered to my door and included an extra lock and 3 sets of perch holders.
Pro-Line (Constrictors NW) is in Washington State.
I've obviously added a lot to it, and use an RHP for heat and a Herpstat for temp regulation.
I'm not sure where you are looking to save, but with BCI's a lot of the time caging is more than the snake. It's also important not to skimp on caging and to remember the pet's best interest.
Considering a cage a "pain to maintain" is not a good sign, no offense but no matter what the snake is in it needs to be kept properly. A drop door or sliding door cage is quite easy to maintain, and referring to it as a large enclosure is a concern. They NEED a large enclosure. Not Burmese or retic large, but an adult boa can be quite large. I'm not trying to be mean or talk down to you, I'm trying to help so don't take offense.
I have to be honest, I loved buying the enclosure and setting it up. It was just as exciting as buying the snake. I took the time to have everything as close to perfect as I could before the snake arrived a month later.
It's well worth saving up a bit and setting up properly. Maybe wait a bit and do it right. You will be happier and so will the snake.
You will never run out of options to buy a BCI, they are everywhere.
Boas are semi arboreal and I think they are happier if they have a bit of room to move and groove.