Growing one big tall plant will be more hassle and money than growing two small ones

lights do not effectivly illuminate tall plants. as you notice the rubber-m grow box it's 1 plant which isn't tall but taking up a huge area.
now thats a good production system

you arn't going to be able to get away with much less than the rubbermaid bin. it's so small i cant understand how you dont have room.

it's your best chance

for your two plants you'd want, about 1 ft x 2.5 ft and at least 2.5 feet tall
as you need room for both the pot and accutal plant's height

an interesting idea is to buy a big rubber tub and put in 4-6 inches of soil. and plant your plants right in it! they could get a nice big root system but not have the height from the pot.

this is dangerious thought, because you couldn't flush the plants if you over fert'ed and you risk over watering if you dont watch what your doing.

other than that. it's a good idea IMO

if you want to see som eplant sizes, we've grown quite a variety. check out my grow log Link in signature