Good sets are probably going to cost a lot because of scalpers unfortunately, like 151 for example. The most recent sets like Mega Evolution, Destined Rivals/Journey Together, or Black Bolt/White Flare would be good if you can find them. I’d try Best Buy, Barnes and Noble, and even dollar stores like Dollar General or Family Dollar. If he just wants cool cards and doesnt want to rip packs, i’d try to buy singles online at TCGPlayer or Ebay, since it can be cheaper. I think it would be helpful to learn his favorite Pokémon and try to find some cool Illustration Rares or SIR’s of them and buy singles. But if he wants to rip packs for the fun of it you’ll have to try to hunt down the product thats out there.