Bob Cohen wrote: <...the cost [of harmonicas] is cheap compared to most instruments, even with trial and error.
I dunno. That used to be true. Now? On a recent trip, I left my road case--the Seydel case with 18 harps in it--in a bar. I retrieved it the next day with all contents intact, but that gave me the opportunity to reflect that there was something in the neighborhood of $900 worth of harmonicas in that case. If I was gigging regularly with it, I might have to replace half or more of the contents of that case every year.
Guitarists pay hundreds of dollars upfront for an instrument, but they don't have to replace the thing every year. Amps and FX cost the same for a harmonica player as for a guitarist.
So is harmonica cheaper? At a unit level, yes--a harmonica costs less than a guitar. For anyone who plays frequently and in public, over the course of a year or a lifetime, maybe not.