Petco and Petsmart are fine for buying small amounts for crickets but if you are planning on buying in bulk it is waaaay too expensive. I usually only buy crickets at most twice a week and usually only 16-20 at a time. That still costs me around 3 dollars. It's not worth it buying from stores, most of the time, you get a better deal online most of the time. But yes, always gut load. Pet stores, whether small or large tend to use horrible gutloads with little to no nutrition or even some gutloads that do harm, such as fish food or dog food. I make my own gutloads and grow most of my own veggies and fruits for the wet part of their gut load.
Healthy bugs make a healthy chameleon. Good commercial gutloads are Bug Burger, Cricket Crack, etc. There are others but these are ones I have heard very good things about. I would ask around if you are looking for others.
I would also start looking into buying some soft bodied worms, and such. Like silkworms and hornworms. They are great if your chameleon is being finicky or you get a dehydrated one or your chameleon gets sick and you need to get some medicine in it. Hornworms grow super fast so it can be an issue, store them in a cooler room and you can put them in a fridge for a day to slow their growth. Silkworms are amazing but they can be hard to raise when they are youngsters, and when they can be hard to get any older than eggs. Both worms have to eat specially prepared foods or in the silkworms case Mulberry leaves.
Wax worms are a good treat on occasion but only like one like once or twice a month. They are good for keeping a good weight on your cham, and just making sure everything stays that way, though they are pretty much pure fat. Praying mantis are a high manteinance feeder, but often worth it just to watch them grow up XD they are amazing. Moths are great but make sure there are no pesticides if they are wild caught. I love raising stick insects for feeding my cham. They are great fun and Ryker loves them. Roaches are great feeders and loved by a lot of chams. Especially green banana roaches. Super worms are good on occasion, I personally never use them unless I've mutilated their mandibles, they can bite the soft mouth and tongue of a chameleon and infections can happen. There are tons of things to feed, and if you are unsure always ask, I'm pretty sure someone will know lol.