The electronic BB is a great idea. Wonder if my college has one by now? ANYWAY:
If that doesn't pan out, you could check craigslist or freecycle or even local thrift stores. And if you want to buy new, you could probably save by ordering online or waiting for one of those super sales at a local chain or store. You'd probably have to get something 10G or smaller. The Petco bookshelf tanks are a decent size (little north of 6G) and do come with a filter.
Don't forget a heater! (Again secondhand or online is the way to go)
For my fish and my plants, I just check the selection at my Petsmart and Petco. They each have a big tank or two with live plants, both potted and bundles. The potted ones seem to do better for me than the bundles. I personally am leery of ordering live things online, cause I cannot be there to receive a package most days.
Good on you for doing your research way in advance though! Like many here, I got a betta first, and THEN came looking for info. You are doing it the right way
Good luck and I hope you get a good scaley pal.