I've never been able to find live food at the stores around here. My betta was in a 20g tank with 3 others. The water is about 82-84 degrees with the lights on (planted tank). I feed them Hikari micro wafers most of the time, but I give them TetraMin flakes or freeze-dried bloodworms on occasion, and peas about once a month. All of my girls have been rather chubby since I got them, but its never been a problem.
The tank does have an algae problem, but I think it is a lack of CO2 for the plants, as algae growth has slowed since I added it. I change 40-60% of the water every 7-9 days, and clean the filter about once a month. It is fully cycled and has been since before I added fish.