Checkout https://once.com/
To get inspiration for the business model. I don’t deny the problem you try solving exists just that I wouldn’t trust anyone.
For one time payment, I agree I will need to implement that.
What feature do you think would be better for bringing trust to you and all users? Because I agree there could be a huge trust issue. I will encrypt the data, but would people trust it?
What about $2 per month to try, if the user likes they can move to $149 lifetime plan?