Last spring, I bought some nice larger pots off of the 50% off rack at Colonial Gardens on 724 near Phoenixville. I haven't been there yet this year, so I'm not sure if they still have a 50% off area, but it may be worth a try.

I don't know what kind of quality you are looking for, but landscapers usually throw out all the pots the nursery stock comes in. They are the black plastic things but if you just want a container, they're fine..... I've even been known to spraypaint a pot here and there to make it a little more presentable!

Try most any "dollar" store. We've bought several 24" pots, kind of that decorator clay plastic look, for about half what you'd pay at other stores. They seem to look and work just fine...