Zelle: effectively instant, requires both banks to be on the network, free. Relatively new and many people who could use it don’t.

ACH: a few days, effectively ubiquitous, very small underlying charge infrequently marked up to ~$3 by the bank.

Wire transfers: not quite instant but close during banking hours, effectively ubiquitous by institution but often a pain for retail users to access due to risk profile, underlying cost is about $5 and often marked up to $15~$20.

The UX of the P2P payment apps is much, much better than any of the above, and would be what I’d reach for for a transfer in the $X0 range contingent on my counterparty being likely to use apps.

Banks in Europe: There might be a fee in some cases but I don't remember paying one (or it's <$5). Rent or similars are just recurring SEPA payments (it's a push - not a direct debt)

But can people (not business) initiate ACH transactions?

Yes. I used to do it to move money between checking accounts at different institutions. I don't think I've ever had an account that charged for ACH transfers. Meanwhile Zelle isn't supported by exactly one financial institution I use (but not one I use for banking).

https://www.mybanktracker.com/checking/faq/ach-transfer-fees...