A service built on a skill you already have
Freelance writing, design, bookkeeping and admin need no inventory or ad spend, so you can test demand this week for the cost of a domain. You are paid for your time, so the first payment arrives in weeks. That first invoice is the single most motivating thing when you are starting from nothing.
The catch: Income stops when you stop. Until you package the skill into a fixed-scope offer or a monthly retainer, you are trading hours for money with a hard ceiling.

