Hi, i know some of country facing depreciated local currency and Exchange control.
Are you talking about countries with weak economy where fiat money is hyperinflating?
What exchanges are you talking about BTC to Fiat or something else?
but i try some online payment, they always charge high rate when i make a transfer or withdraw.and they will charge some hidden fee.
What online payment are you using? Fiat based centralized service?
If you are not pleased with the terms of this service just stop using it, find another one, there is more way to transfer your money that just one service.
so any better options which charge low rate?
Yes using cryptocurrency. Unfortunately if you are looking for near zero fees then Bitcoin is not an option anymore as standard transaction will cost you almost $1. (55k satoshi)