How many plants?
if it is just one(max is two anyway and its generally too crowded) then i would go with a rectangular tupperware box. Low sides but it should take up most of the bottom. Make internal measurements then go to walmart and pick one out. Then drill some holes in the bottom for drainage. The roots will go sideways as well as down, so it can help there. Gotta figure in that your plant max height goes down with every inch of pot.
You could use a two or three gallon smart pot(or make one custom) and then just trim it so it is not as tall. A smart pot is a fabric pot that promotes good root aeration and also allows you to grow bigger in a smaller pot. The theory is that the roots grow straight out(as with all pots) but when it hits the pot instead of turning it goes through the pot and then when it hits the dryness and air of the outside world the roots get pruned off, after which the roots grow shooting off that root as feeder roots.
Ultimately this is meant to prevent root locking, where the roots swirl around a small pot too much and eventually run completely out of room.
