Unlimited cards aren't necessarily where you're gonna find the best deals, honestly. The basics are still affordable but people know it's coming back in style and prices have gone up compared to a few years ago. That said, you do have options. Flea markets and garage sales are really your best bet for this - I found some cool stuff at crazy prices just because the sellers were just trying to get rid of their stock. The thing is you gotta get there early and actually check the condition of the cards, not just take the seller's word for it when they say "good condition."
Otherwise online, eBay is still solid if you know how to filter the listings - there's legit stuff and total garbage, so look at the photos and seller reviews carefully. Facebook groups specialized in your area are also a good angle, usually lower shipping costs and you can negotiate. For specialized physical shops, you'll pay more but at least you can check the cards in person and avoid nasty surprises.
My suggestion: combine everything. Wait for local flea markets, hunt around on eBay for bulk lots, and ask questions in local groups. Also look for lots rather than individual cards - you save on shipping and often people give group discounts. And don't be too picky about the condition of really common basics, or you're gonna spend way too much money on it.