are you indicating that for the PAIR (cabinets and speakers) $150 to $300 is the going rate,,??
I believe he is, with the emphasis being that the bulk of the value is in the 420 bi-flex drivers.

Some of us DIYers will sometimes pick up Madrids and Santanas on the cheap as they provide a well made cabinet with a removable baffle offering many project possibilities.

The 420's are more easily shippable than the complete system, and resell for enough to recoup the initial cost plus a good bit toward new/other components.