No Petco or PetSmart around huh? I'm not a big fan of them but when ya need stuff and have nowhere else to go....annnyways, dividing them is a way to go, for 6 bettas you'd need to have a 20 gallon with 5 dividers (if you wanted the filter intake to have it's own spot you could still pull it off, just 6 dividers, kinda pricy but maybe still cheaper than running 6 Mini-Bows). Each of them could maybe have a plant too-silk ones.
Do you have any Wal-Marts or other stores around that sell Mini-Bows (we have Meijers but that's regional). Do not buy that Aqua Tech crap if you buy from Wal-Mart. You'll just end up upgrading which means more money.