It's very simple, just don't make it accessible outside your home network. Clients sync when the server is accessible and use last synced data otherwise.

The effort required to set this up far outweighs the price to pay someone to do it for me.

I pay a cleaner, I have a dishwasher, I pay someone to do my taxes, I pay for companies to host software.

Then again, I never order food and almost never get takeaway, as cooking is nice and I value my food enough to care what goes in it. Cheaper too, easily offsetting what I pay for my password manager.