This will immediately bias the submissions only coming in from the west. Remember you can make the fee small but sometimes a person can't even pay even if they have the money. I remember having the 1000 or so rupees required for some VPS stuff when I was a teenager and not being able to pay since I didn't have a credit card. I hope we don't ever make money a barrier to open source.
Then make some other very cumbersome proof. But it's still better to cut off half the world from open source than pollute the few large software repositories with spam, which would dissuade everyone everywhere from contributing eventually. There's no problem contributing to a library from anywhere it's just that you collaborate with someone who in turn can pay the reg/anti-spam fee.
The reason money is natural is because there is a cost associated with manually vetting all packages.
I doubt it.
It's easy to get a Visa/Mastercard in the US. It gets a bit trickier in some EU countries. Then the further from the west you go, the more complicated it gets, all the way down to impossible if you live in a place that the US isn't on friendly terms with (like Iran or Russia).
If you auto-assume everyone can pay any amount online (even if it's a refundable $1 for verification purposes), you're gonna cut off access to a lot of people unintentionally, while only raising the bar a little bit for spammers.