Question about pot size

I've got the run-of-the-mill rubbermaid grow box like you've seen all over these forums, and I was wanting to grow 4 plants in there. If the plants will only be around 29 inches final height, what is the smallest pot size i can get away with without having rootbound problems?

Also, what are some cheap pots, or some cheap ways to make your own pots?

well u could buy a 2 liter bottle of soda and poke holes in the bottom. although id cover the outside surface with something so light doesnt get to the roots.

Well for one.. you go to a local plant shop and i got my posts 4 gal for 1 canadian dollar super cheap.... if your using all female clippings i would toss them into a 10 gal rubber made container.... 4 of them anyways.... other thank that pots are cheap man even fancy ones are only 5 bucks

All I can ever find are round pots made of either really thick plastic, or tera cotta. I'd like to find some nice plastic square ones to cut down on space issues.
Again though, about what size could I use?

you will need about a gallon of pot space per foot of height(of the plant)

Aight, thanks man