I found myself in a similar situation with a budgeting app I wrote. Initially I was planning to make it public but the idea of dealing with people's financial data and paying for all the infrastructure caused me to change my mind.

Instead I've been exploring a strange idea of using sqlite client side. People would save their data to a sqlite file that gets downloaded, then when they come back, drag the file back onto the browser to pick up where they left off. A little awkward, but 100% client side, side skirting most of the problems.

(I realize hardly anyone would bother to use this app. But making it public with sqlite is really just an experiment. I host the app on a raspberry pi inside our home network and we use it that way.)