There should be a revote/caucus or nothing.
Vote by mail, seems cheapest and easiest to accomplish. I participated in an absolutely hellish caucus in Kansas, and think it's undemocratic and disenfranchises voters. I'm fairly young, but I was standing in sleet in the cold for an hour, then waiting for an additional 2 hours to be checked against the voter rolls, then standing an additional hour for the caucus to get organized. All told, some 4 hours on my feet, my legs and joints were in terrible pain. Elderly people, the disabled, and parents with children were forced to abandon their right to vote because of it. I've never seen anything as shameful. Caucuses should not be permitted to determine any re-vote, and should be abandoned out of general principle.
It doesn't need to work like your caucus did ,though.
A caucus is party driven, even if you go in and vote just like a primary. New Mexico held this sort of caucus.
A primary is state driven.
Why is a mail-in vote funded by the Dem party not an option?
That is an option. It would be a mail-in caucus.
And do the people who jumped shipped and voted in the Republican primary also get to participate in the Democratic caucus? That wouldn't be right.