Have you any ideas what tools might make your (dev) life easier? You can create a small productive/utility SaaS app. Use bootstrap if you don't have any design skills. Use PayPal/Stripe to setup a (recurring) payment system in a day.
Test using lean methodology, buy a domain, create landing page with bootstrap, pricing page, and a fake sign up page. Takes max a week. Then spend another one week driving some traffic from Google/Facebook ads to see if there's any interest. Usually Facebook, if targeted well, is way cheaper. Start using Google once you know your LTV (Life Time Value of customer) and conversion. Start by spending for example $20.
One tip: Don't target US customers in Facebook for polling interest, they are harder to convert, and from my experience around 10x/20x more expensive than Asian/Spanish speaking countries.
After you see interest, try to find a quick way to see if people are willing to pay. This might not as easy as most users want to use your product before paying. You might explain the product in better detail after the signup and ask what they want to pay for it.
After you are able to confirm if people are willing to pay for your service, only then spend serious time building.
You can apply the same tactic if you're selling an e-book, maybe the spices idea as someone mentioned before.
Good luck!