$1/mo x 12 months x 10,000 customers = $120,000
But that will not pay a modest developer salary. The corporate side of FICA is 7.62%. Also add in health insurance, a retirement plan, office space, a computer for the developer ... and that's just the human side. There's all the corporate costs (e.g., servers) and regulatory filings.
The only play I can see with something like this is to ride it out and hope some established player buys you out for the tech.
