I used tubs for the first few months of my burm's life. Cheap and cheerful. They'll outgrow 'em quick, so be prepared to bump up to a 4x2 within the year.
. . .or you could also go straight for a 4x2 and just provide lots of hides and features for the snake to feel less exposed. That might actually be a better option. You're building/buying one anyway.
When you do get your burm, pictures please!