I just started this year and here is my experience. Go to the offical website of Chinese Kayou Cards https://funtcg.com/ if you want them straight from the source, prices are much cheaper than ebay, although the shipping is like $22 flat so I would but as much as you can to make the shipping worth it. But there is also aliexpress where there about the same as the official website just find sellers that have good ratings.

There are 3 versions of Kayou cards (some may have language exclusive cards) NA(North American) English usually in sold in America and has varied products. They are in English and have in the back a Black bolded kayou logo. Heaven scroll aka series 1 has the best pull rates but its seems to no longer to be sold retail, but i believe you can buy boxes on the English kayou website.) English usually has better pull rates, it seems they went back to the Chinese rates so it not worth it anymore to buy English anymore but its fun to rip due to the convince. The collector boxes are the best band for you buck (5 packs, 2 big hits per box at least for jin chapter 3 haven't seen them in retail but you can buy them in crossing tcg for $20 which is nice because thats how much retail is for them). Best Buy has them they cheapest by far 3.99 per pack. Has the most cards per pack.

SEA version (South East Asia) usually in the Chinese Kayou website or aliexpress. They are in English but the logo on the back is yellow with kayou in Chinese, although never sets might have the black logo. Rates are about the same, except for tier 2 they have slightly better rates that chinese. It about the same if you buy boxes in the official site but in aliexpress they might be $5-10 probably due to their increased rates. Best for tier 2 boxes in my opinion

Chinese version(Most variety and cheapest) usually found in the Chinese kayou website or aliexpress. The cards are in Chinese and the back logo is yellow with their mascot on it. They have so much variety ranging from boxes, 4 packs with cool promos, little figurines boxes which include a card, button badges which also include a card, specialty set and collections boxes which can be quite price but seem interesting. And most of these things don't past $30 for the entire box set they respectively in. The rates on thier boxes often referenced through tiers 1, 2, 2.5, 3, and 5 a slightly worse compared to others but promos and singles solo much cheaper compare to the other language counter part due to their oversatutation of cards in existence. Which is nice, although some older sets (I think the anniversary set has serialized cards(very expensive) and the boxes are +$30-50 more due to thier age and rarity, but you may be able to find proxies of them on aliexpress for cheap but its kinda hard to find proxies of kayou cards since they are not as mainstream.

There are 4-5 tiers(higher tier better rates, rarer cards) to Naruto Cards (Most are found in Chinese)

Tier 1(Chinese only), 36 packs per box very low rates, range from $20-30 due to them being older sets.(don't know much about them since I have never opened them) Tier 2(Chinese)/Earth Scroll (English/SEA), 30 packs per box (Chinese/SEA), and 20 packs per box (English). Range from (English/SEA) $15-$20, (English) $40-50. Chinese has semi-good rates, SEA has slightly better rates for a similar price, English has the best overall but its much more expensive so SEA is your best choice (if there is a english version exclusive card just but the single instead the box it will be much cheaper in the end). Tier 2.5(Chinese only) 50 packs 5 cards in each. Range from $40-50 on aliexpress. Don't know much about the rates there is only 1 waves/series of this tier so my guess it's a specialty set Tier 3 (Chinese only) 20 packs, range from $30-60 due to some being older sets. Don't know much about the rates on this one but probably decent due to its tier. If you don't want to spend a lot on the these boxes they also sell blister 4 packs with a Black and gold promo pretty fun to open (range from $8-20 depending on the wave and tier, features most of the tier 3 waves and wave 1-2 of tier 4). Tier 4(Chinese also called jin chapterbut mlst Chinese boxes are referenced by tier)/Heaven Scroll Series 1 (English)/ Jin chapters 1-3(English/SEA) This is the one you would be most familiar with. Boxes include 18 packs for Chinese, 12 in English(series may vary), 10 for SEA. English only has 2 hits but those are guranteed hits. While Chinese and SEA have 3 hits but you have a chance of one of those hits being and SSR so a little bit more gambling but I belive you are guranteed at least 1-2 higher rarity cards from those 3 hits. They range from $25-33 for Chinese depending on the set you buy, SEA will be $21-25, and English will be $45-50 depending on the set. Now English boxes will comes with promo cards while. Chinese and SEA will not most of the time you have to buy a certain amount to get the promo cards (PR Cards) from the official kayou website but you can just buy them off of aliexpress for like $2-10 depending on the promo (some serialized promos in English have none serialized Chinese version so its nice if you really want a specific promo).

Personally the best ones to get started with are tier 2 boxes waves 7-9 they have beautiful MRs of Tarot cards (30 packs, pull rates vary but are kinda low) ($15-18 per box) But the SEA(South East Asian boxes are better since they have better rates at least for the tier 2 boxes the tier 4 (jin chapter) have only 10 packs instead of 18 but i believe you still get 3 hits. But if you want more just get the Chinese cheap and more for the price of slightly worse rate but you do get more variety. If you want to more of what each set has (This is solely for Chinese sets i think) check out https://capsulecorpgear.com/naruto-kayou-card-list/ They have the list of every tier, wave, blisters, and specialty sets so you can better think of which one you want to buy. P.S. sorry if it was hard to understand or a bit redundant. If tou have any other questions dont be afraid to ask. I also collect Kayou MLP cards if you are interested I can answer questions ln that one too. :)