I'd keep in mind that even though someone may find an activity profitable, it's often largely affected by the local laws and tax policies.

For example are a myriad of 10s-100s of bucks/month I could theoretically make that have demand and in many countries someone might do, but here it's

1) required to have a company

2) static taxes are several thousand/year

3) dealing with requisite liabilities and insurance lifts the monthly fees to some hundreds/month

So check those first before diving deep

All of those things are optional.

I promise you can sell something to your neighbor for $10 without filing taxes and registering a company.

To believe otherwise is like the Top Gear story about the German guy who insists you need a license to drive a car.