in the season. I bought what was supposed to be a "Mr. Stripey" at a plant sale, but when it started fruiting, I had little red grape tomatoes. Late in the summer, as the grape tomato was slowing down, large tomatoes starting appearing, but they never got going. I think the "parasite" grape tomato took all the nutrients.
I wouldn't plant two to a pot.* Do you have Freecycle in your area? (freecycle.org)? People are always giving away pots on my local board. You can also post a "wanted" and see who might have extras to spare.
Home improvement stores sell 5-gallon buckets for a couple of dollars, if you don't mind drilling holes in them and their less-than-pretty look. Sometimes chain restaurants will give away the 5-gallon buckets things like potato salad and pickles come in (again, hole-drilling required.)
I had some great bookmarks on growing tomatoes in pots, but my laptop died, taking all my last year's research with it. :(
Here are a few I've recovered so far:
http://www.bellaonline.com/articles/art19000.asphttp://organicgardening.about.com/od/vegetablesherbs/a/tomatoescontain.htmhttp://www.tastefulgarden.com/store/pc/Growing-Tomatoes-In-Containers-d9.htmHope they help.
*
And remember that clay dries out faster than plastic, so you'll need to water them more often.