If the buying a domain part is outside your budget, consider gelocalcert (I work on this) or one of the other free subdomain providers [2].

[1] https://www.getlocalcert.net/

[2] https://free.wdh.gg/#/?id=domains

> Orrr just buy a domain and get a wildcard LE cert?

If you have dozens (or more) of locations that need a cert, then on a yearly basis you have to run around updating things.