With a little extra in the cage to make it seem smaller a 3'x2' would work, it's obviously not perfect, but it will work. I started mine in a 2.5'x1.5' sweater box to start and ran into no issues there.
And also yes, you were given false info if you were told that ALL baby rtbs are snippy. One of my was the first week I had him, my other was the sweetest little thing from day one. You can't ever definitively say that ALL of one type of snake is going to act a certain way, they are all individual living things after all and will have their own personalities. Just like some never tame down no matter how skilled the owner is, that's just the way things are when it comes to living creatures.

Also, not sure what you consider moderate as far as price goes but I know I personally have fallen in love with a lot of the different bees out there if I had the spare cash I'd have one in my hands right now.