I run https://www.goread.io/ which is a subscription-based RSS reader. It's open source and runs on google app engine. It costs ~$2k per year to run and I make between $2k and $3k profit per year for nearly zero effort. Stripe handles payments and app engine keeps the servers running.
I consider it a high success because for the amount of marketing I've done in the last 2 years (exactly zero), it still has paying users. If I did a few months of code improvements and marketing pushes I could probably increase that income a few times.
In 2015 I paid app engine about $1700 or ~$130/month or a bit over $4/day. I could probably get that down another dollar or so a day if I did some optimization and cleanup work, but I haven't cared.
Hmm just as a side-question. Do you consider the time developing this product as a part of the "expenses" sheet?
I'm asking because I did some side-gigs in the past and I always end up having a product ( aff.links ) that pays the server and some pennies above, but if I count the time lost on developing it, I will be on severe loss for decades.
I did not count my own time, no. If I did I'd almost certainly be below profitable. But I was doing it at the time because I wanted a google reader replacement, not to make money. I only started charging because I had so many users (at the time, most are gone now) that it was costing me above $50 per day, which adds up quick.
Trying it out now. I hope I'm hooked enough to pay you at the end of the trial. Not really satisfied with my current solution, which I also pay for. Thanks.
I consider it a high success because for the amount of marketing I've done in the last 2 years (exactly zero), it still has paying users. If I did a few months of code improvements and marketing pushes I could probably increase that income a few times.