My only cost in feeding is the beardie/turtle salads.
I have 2 colonies of Dubias for anything larger, and 3 colonies of mealworms for the smaller critters.
Feeding the bugs is extra catfood ground in a blender and leftover veggies for the dubia, the mealworms get their substrate and potatos or carrots, depending on what we have as leftovers from dinner for the week.
The real cost is in the heating/cooling. I keep a stable temp of 75F overall is the entire house. The bad part is, in the winters, we get into single digits, during the summers we do triple digits.