You're trolling, right? Everyone knows that there are generally no "actual numbers" available for this kind of transfers unless you're a BigCo or a private banking customer.

You'll send $1000 from your Nigerian bank to the Peruvian bank, $937.65 will arrive after a week+. Most likely nobody will be able to explain where the money went.

No, I really am asking a person to provide facts to back up their claims. I was not aware this was considered trolling.

There are no useful facts to provide, outside of strictly regulated markets banks pull these fees out of their asses. The receiving bank might charge various mystery fees, so even if your bank is playing nice they won't be able to tell you how much will actually arrive.

It's just almost impossible to know the answer to the fee question beyond "probably a lot"

"Likely" because for the scenarios/markets where international payments work poorly there's no "actual numbers" in this situation, the pricing is highly dependent on circumstances, the specific institutions involved, the currencies involved (there may be multiple, and for some countries a currency conversion may be mandatory), the payment scheme involved (depending on the country/bank pair there likely will be multiple payment channels with different price/speed/reliability tradeoffs) and who is paying (which affects a lot the prices you may get). For such deals the sending institution will generally refuse to quote a fixed generic price, because the price will be different depending on all kinds of factors that, in some cases, will be revealed only after the payment is delivered or returned.

An bank payment from Nigeria to Peru might reasonably cost $20-$100, and I wouldn't be that surprised if in a particular situation it would come out to $10 or $300 (like, making a typo in some field of a non-validated foreign payment, or having an unclear tax situation on the goods for which the payment is held - that can easily cause e.g. a $100 extra unexpected processing fee for the payment). Also, you may get amount-proportional fees, and a 0.5% fee can potentially be huge for larger payments. On the other hand of the comparison there is also significant variability for the extra costs of the cryptocurrency payment - as the original question stated, including the cost and exchange rate variation of buying crypto for fiat in the sending country and selling crypto in the receiving country.

So it's likely but not certain that it's more expensive than an equivalent crypto payment + the to-crypto and from-crypto conversion, it depends on unknowable circumstances, and the variability and unpredictability of such fees is a big drawback on those types of international payments - unlike e.g. the intra-EU case where the fees would be predictable and low - perhaps zero, depending on your bank.