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.
To save others a search, the Top Gear story (it's only 40 seconds):
https://www.youtube.com/watch?v=B3EBs7sCOzo
Aside from that - as for parent poster's story about needing to register a company, perhaps they are living in a particularly onerous jurisdiction. But more generally, many jurisdictions allow you to be a Sole Trader with fairly minimal registration. Filing taxes - well, hopefully you do that already, and adding your Sole Trader income is likely not that much work on top. (Selling overseas and dealing with overseas taxes? There's often companies that will handle all the overseas taxes on your behalf, and they might only take 10% or less of the sale with no upfront cost as payment.)
If you're not sure about this stuff, see if your city has a Small Business Development Center where you can ask their advice. This stuff is probably all online, and if not they might have leaflets & books on what you need to know. Places like that will often have open hours with someone from the Tax Office as well where you can ask your questions.
Especially, don't put up walls for yourself that weren't already there. This stuff really may not be as complicated as you think.