You should be able to get a few at a local LFS for next to nothing. You'll only need a couple and before you know it you will have more than you know what to do with. If you strike out at the LFS I'm sure someone will throw a few in a baggy for you.
I started out with 0 a couple of months ago, bought a few plants at PetsMart, and then a couple snails that hitched a ride decided to start a family. Now I have plenty in my 55 & 12 gal. tanks.