Im kinda wondering what your doing with a 6" pot. Would a large size plastic cup do the same thing. A seedling can stay in both about the same amount of time before needing replanting. It would be the cheapest.
As for bigger pots, I too look for landscapers, check freecycle etc. The one gallons are the easiest to get, but its the 3 gallon and up Im after. They are harder to come by.
