WHEN BTC -> FIAT is too expensive?

HI everyone.
Years ago I was trying to get into crypto.
Fund that it was really hard to find a way to buy with fiat, even worse, living in Mexico, the exchanges were too concern about money laundry and so on.
Back then I found that exchanges charge with at least 20% of each transaction mostly when a user try to move his crypto to his own wallet.

Any way today I just create an account with Binance and found that it is possible to “buy” crypto by P2P on my own country transferring fiat to a bank account, and after confirmation the crypto offerer transfer the coin to my binance account.
Ok it works… BUT … it was expensive… I mean. It was 20% more expensive so at the end the same situation arise.

I know there are hodlers here and I agree that if you turn your crypto to fiat you should look for a “gain” but it is there any rule that will keep me spending 20% more?

Thank you guys for your answers on advance.