Looks like Wikipedia actually has a decent section on it: https://en.wikipedia.org/wiki/Diaper#Debate
These are prefolds, with outers: https://www.amazon.com/gp/product/B002LR8VC4
Prefolds are similar to the old flat nappies but they're thicker so you don't have to fold them so much. They work well but they're not as simple as the other options:
These are pocket: https://www.amazon.com/gp/product/B00SWIA5LQ
They have a pocket in them where the absorbent insert goes. Easier to use but usually not quite as absorbent as prefold.
Then there are other variations, e.g. Ones where the absorbent inner clips onto the outer ("snap-in"), or even simpler ones that are one outer and inner combined ("all-in-one").
Pricey new, we bought 30 of them used for $50 bucks on craigslist and soak/cleaned/sun dried them for a few cycles.
I loved the all-in-ones.
https://www.aliexpress.com/item/free-shipping-100-cotton-wat...
The top result I got was a Walmart ad. The "Gerber It's a Snap All-in-One" is $9.98 for 3, so about $3.33 each.
I've seen them in physical stores as well.
- If you'd really prefer modern style cloth diapers (prefold, pocket etc) instead of the cheap old-school flat diapers, often you can buy second-hand ones that are hardly used (or not used at all!).
- If you have any more children, your cost for buying diapers is now $0 because you already have them.