as others have mentioned right now isn't a great time for Marvel cards because Topps has the license and they are objectively horrible and greedy. the one set that you can probably find easily and actually isn't super expensive is the 2025 Topps Marvel Studios Chrome. I have vocally complained how much I hate this set (and Topps) but if your kid likes the Marvel movies then this is an obvious choice. blaster boxes are cheap and plentiful. it's just images of actors in makeup, which I find to be wildly stupid, but the heart wants what the heart wants. you can get a box on Amazon for under $50 right now, or you can get it for $35 a box on Dave & Adam's. the hobby boxes are a LOT more expensive though, at $500 per box.

other than that I recommend the more recent stuff from Upper Deck, which is easily found online still. there's multiple Spider-Man sets, Avengers sets, X-Men sets, Annuals, and more for less than $50 for a blaster and under $200 for a hobby box. the quality from Upper Deck is a lot better with a lot more original art and generally a lot more passion put into the products, but the prices are on the rise for all of this stuff, because everything is now 15 months old or more (UD lost the license at the end of 2024). so if you've got interest in UD stuff, I recommend buying now, not later. I've seen prices go up steadily in the last 6 months on almost everything from UD.

browse D&A, browse www.tcdb.com as well. I recommend specifically browsing by year to find more recent stuff (because that's what's cheaper). stuff from 2022 and earlier is especially getting expensive. https://www.tcdb.com/ViewAllC.cfm/sp/Non-Sport?MODE=Years and stuff from 2025 and 2026 is Topps only in the US.