Feed snails, crayfish, half shell clams, krill, prawn, shrimp, etc. I wouldn't bother feeding pellets, puffers are messy enough without adding pellets to the diet. I've had some puffers accept pellets and there was just powder flying out of the gills. Krill is great food for puffers, it doesn't have a very hard shell, but is still healthy food. Offer a varied diet and it should be fine. SAPs are the only puffer that requires crunchy foods for every single meal.
I have a small tub that I breed crays in, and a 30g planted comm tank that I breed ramshorns in. I feed the snails and crays lots of vegetables to benefit the puffer. If you can get 5 apple snails for $1, I wouldn't even breed them, just buy 5-10 a week and make sure that they are appropriately sized.
Just my opinion.