I prefer getting them online from rainbow ^^
The reasons I prefer rainbow are, I know they are raised in safe bedding and they are affordable and intended to be fed to pets.
The reason I wouldn't use bait shop mealies....... you don't know what kind of bedding they have been raised in or what they have been fed.
Corn based bedding has the risk of producing aflatoxins. For bait aflatoxins aren't really a concern, for gliders it is a huge concern and can be deadly.
Same goes for crickets.
If your going to feed live treats to a pet, it should be intended to use it for a pet by the source. Bait is intended to be used as bait....
Personally I Don't like pet shop mealies either because they never know where they come from or how they were raised before coming to their store and they are more expensive and don't go as far as rainbow mealies do for me.
I get anywhere from 200-500 at a time and put them in the fridge, at my highest amount of gliders (12) This would last me a month or two, I typically only feed mealies for nail trimmings.