There has been a discussion in the YamahaDX Yahoo group about moving to groups.io, and the admin of that group has now started the process.
Fees start from zero, for upto 1GB. To transfer a group using their tools takes a premium account, which is $120 per year, but a group can be downgraded after the first year, to a free one. It can probably be done manually though, apparently, with a free account.
groups.io has a fairly uncluttered user interface. A blind member of the YamahaDX forum said she found it okay for accessibility - unlike Google Groups. I suspect Facebook might be a problem for that too.
Here's a quote from the YamahaDX group, which I hope the author won't mind me reposting. It seems several related groups have already moved to groups.io:
"YamahaQY70AndQY100 has their Groups.io group up and running. Only 11
members so far. I’m not sure how big it is on Yahoo. VintageKorg is up with
Polysix, Drums, MS-series and Tape subgroups. I believe MonoPoly will be added
next. Poly800 is thinking about it.
The Polysix group did a GoFundMe to get the funds for a year of the premium
service in order to get the migration tools to get everything from the Yahoo
group. It took one day to get enough money. They started the new group as
VintageKorg and made Polysix a subgroup...
Don B."
- Andy