Technically, if he had enough time, your friend could have bought UA or UR for about 1.7cpm (the apparent market rate). However, the excess .38cpm (or $100) he was actually charged over that rate can possibly be chalked up a "last-minute surcharge" as you supplied them precisely when he needed them.
Then again, you did save him $400 if gauged against prevailing revenue tickets.
Interesting Q.