The 22mm EF-M lens was only cheap because the first generation EOS M was a commercial disaster in North America. You paid the equivalent of a clearance price.
Only somewhat. Look at the 24mm, 40mm, and 50mm STM lenses ($150,$150, $125) which are about the same complexity as the 22mm.
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Erik
Of those lenses, the 40mm is the standout, as it's sharp wide open and has almost zero distortion. The 50mm STM isn't cheap as much as an old fashioned 50mm F/1.8 that doesn't get sharp until F4. The 24mm is the only dedicated crop circle lens of the trio. Personally, I think that full frame 24mm pancake would have been worth a lot more than $150.
The EF-M 22mm was going for $249 before the EOS M firesale. I can't remember if that was the original MSRP? In any case, I'm not sure what that says about the relative cost of crop circle lenses. Actually, I don't know for sure that the 22mm doesn't cover full frame, although I think it's highly unlikely. Either way, it wasn't intended to be a $100 lens before the EOS M clearance, much in the same way the EF to EF-M adapter wasn't meant to sell for $50 but originally was priced at over $200.