A mirrored letter still looks very similar. Most people learn the letter topologies first, and only later pin down the chirality. Just think of all the mirrored N's you probably used to write!
So it's definitely not twice as much work, I'd say it's not more work at all, you basically just don't worry about the chirality and that's it.
No idea what the relative cost of those are but I'd wager it exceeds the mechanical cost of scanning back to the "front" of the line...