I go to craigslist too.
Over the summer I got a 10 gallon with hood, light, substrate, and filter for $30.
I bought my 5 gallon myself for about the same price, and right now I just found a 5gal marineland Hex for $20.
It comes with the whole shebang.
Also the large/extra large kritter keepers are cheap and there's a great deal on the right now:
Medium is about 3/4 gallons, large is about 6/7 gallong, Xlarge is about 10 if I remember correctly.
Great tanks when you add substrate and heat.
Naturally planted Kritter Keepers wouldn't need a filter either, or very many water changes.
(YOU DON'T GET TO CHOOSE THE COLOR OF THE LID but i don't care much about that so i didn't mind)
This is a 5 star
review by a betta keeper:
Kritter Keepers Are Great
By Tab from Mount Pleasant, PA
On September 8, 2009:
Love the kritter keepers. They're great for my bettas who are much happier in their own homes rather than sharing a divided 10 gallon!