Tropicannas - you can useally find a good deal for these on ebay. I talked the people at home depot to take over 50% off their Tropicannas. It didnt work the second time I asked though.

Stuttgarts - this is harder one to find for cheap. Dutch bulbs sells some 2 for $10, however currently they are all out till spring. Hugh's water garden shop (www.thewatergardenshop.com) seems to always have some available. I ordered from there and was happy with my purchase. The prices I see on ebay for Stuttgarts is crazy!

These two are more sought after. If you put a post in the exchange forum you might find someone to trade with you. As a matter of fact, I might have an extra Tropicanna, do you have anything for a trade?