> transacting fiat currency generally costs a vendor ~3%
1. Bitcoin is no less a fiat currency than the U.S. dollar or Japanese yen.
2. For small retail transactions, yes, 3% seems right. Larger transactions, however, are generally done by wire. These transfers carry a fixed fee and are generally a very small percentage of the transaction value.
> 1. Bitcoin is no less a fiat currency than the U.S. dollar or Japanese yen.
Depends on what you mean by "fiat currency", which tends to get used with a few different (if related) meanings. One is "non-backed state-issued currency". Under that definition it isn't. Another is "currency with no intrinsic value". Under that definition it is.
I'm not sure if this differs for six-figure transactions, but transacting fiat currency generally costs a vendor ~3%.
Receiving bitcoins and immediately converting them back to USD/GBP can be done for less than one percent of the amount of the transaction.