rick,
here is my opinion.....
at $400 I believe you could easily fill a niche market, have custom engravings and custon serial numbers as well as HK/POF like safe/fire markings on the lower, seriously for the $400 + Cost plus for the extra engraving I bet you would sell 100-200 lowers a year.....
the question is "is it worth it to you to be a low volume custom manufacturer?"
I would buy one to donate to the next IDPA provincials if it could be engraved for the occasion.... I look forward to see where you go with this, at the very least it can use your free time on the CNC machine and all you really need to produce is 1-2 a week in the spare time.