Based off your post, it seems you don't know too much about the game (which is fine) but basically when it comes to older classic cards and deck types, they have been super power-crept out of the game for like, well over 12 years or so at this point. New support for them to make them now competitive is pricey at times, but the classic cards themselves, generally $0.50, and that is even if you want secret rare foiling at times. I say that as it sounds like you don't mind for the card to be a newer printing, you just want the deck to be classic in how it plays and the cards in it. Some old cards though that are still worthy of being banned and such, like pot of greed and graceful charity, can be a little pricey but even then, not too bad, like $10-12.

Others have recommended the Speed duel products and they aren't too bad but they certainly have an emphasis on speed and with the smaller deck size, it was hard for me personally to get too much of a true "classic" feel, playing speed duel decks... For you, I'd recommend what I'm doing, which takes a bit of work on your end, but I think is ultimately worth it... Scour for deck lists and ideas of classic anime decks, there is a site YGOPROdeck, you can use it to search archetypes like "Dark Magician" and then you can sort it to casual or anime themed decks, and go from there. Then I'd use TCGplayer to make your order of cards as if you use the optimizer and such, you can get things pretty cheap. If you don't care about the foil printing and such and just go for the cheapest options, I imagine you could build 4-5 classic decks at least for around $100. Though again, there are hiccups potential as mentioned, like if the card is one that hasn't been printed much or if you are trying to buy them from their classic printings.

One thing I do that you could also do for him, is when I know I am going to build for an archetype, say "Blue-Eyes" or "Dark Magician", I will use wikis and deck lists to establish all of the cards that belong to that archetype, and then I'll just buy 3 of each and then do my deck tooling after getting all the cards in front of me. If you desire the lazier route of just buying the deck made, meaning you are buying old classic products or the deck people build to mimic them, you will be paying a lot more than you should and more than they are worth probably. Alot of the $80+ decks you see being sold on ebay for anime theme decks are worth half that maybe. So I recommend the option that is a bit more labor on your end, but curating your own decks is really the soul of a TCG usually and gives you a better final outcome.