Or you can check other forums for items for sale/trade. I got my first plants for my current 40gallon breader tank for $20, and that included shipping. I could not plant them all, and traded about 1/3 of them to my LFS for store credit.
When I did 8 tanks up in Iowa, I sold clippings to friends, just for the postage cost.
If you do a 'grab bag,' you will not be sure of what you get. You need to know a bit about plant structures (so you don't bury rhizome plants in the substrate, etc.), but its fun (to me) to see what you get. You won't have things individually labeled so you must do some research once they start growing to see what you ended up with, if you are curious.