I've always thought the limiting factor wouldn't so much be cost as weight. Those full sets of harmonicas must weight a ton.

I've always been one to have just one or two harmonicas in plausible keys. Best I ever had was a doublesided one from Brazil I picked up for four or five quid from a street trader at a Fleadh. Gave me G and D playing straight harp, which was fine for my kind of sessions. But I mislaid it in a pub after a few years. I hope whoever picked it up valued it. Never seen one like it.

But then I've never been a serious harmonica player.