I don't agree 100% with your statement about cost. D-Box's price compared to other "high end" equipment is fair unless you need to install into a lot of seats. I am comparing against items like $25K+ for high end projectors that are obsolete in a few years (480P->720P->1080P, 3D, 4K, etc..). In retrospect, there have not been a lot of advances with D-Box tech. Typically, costs go down as tech ages, but not so for D-Box. I know this is not a 100% fair comparison, since these are not apples to apples. D-Box has mechanical parts and it would probably be more realistic to compare to something else but there is undoubtedly a decent margin built into their price structure.
As for used market, how about 2 seats, full turn key for $3500 + shipping?Ebay
I know there have been other deals as good or better.