Within the Axiom line, my experience, so far, is $ = quality. Perhaps within each individual line of speakers of the same company, $ = quality. Just not so across companies, $ wise.
What about size = quality, because that is one reason why cost goes up in a line as well. Hence, does the world's largest speaker automatically sound better than anything smaller?
If you price out the M50s which are more expensive than the M22s, i think the M22s have a better sound quality. You could qualify that sound by a more linear frequency response if so inclined.
I certainly don't think you can literally line up every Axiom speaker from lowest price to highest and then qualify how each speaker is somehow better with every price jump.