I think even if the bitcoin price varies you should determine the fee in the count of bitcoin not in USD, crypto is not a country that must use USD
sincerely ... i would have to agree fully on the idea of this ! for first thing= this is a Bitcoin forum and not a USD forum. and if they ever have more then the single "1" person who signed up = i would assume that many will not be from the USA so unless this is a restricted sig campaign for the United States only: they should be using Bitcoin.