Jacob,
Last year I sold tomato and pepper plants, that were nice size, in 3" containers for $2.50 and had a lot of people happy to pay that for them. Didn't really cost me much at all, a lot of the seeds were left over in the packet, a $15 bag of potting soil was enough for about 200 plants and the containers were less than a dime each. Counting electricity, the total cost was under a quarter per plant.
Mike