Glenn, I think this is an excellent post in that it shows that the volume wholesale discount on all of the pieces & parts when a shop is building a dozen (or more) at a time really makes the decision easier. Also most interesting is that you've included zero for machining, assuming that you can get it machined right from Summit. The price difference running $6013 vs $4600 is a 23.5% discount, but that $4600 includes something for labor so I'd say that it's at least 30% average discount on the parts.
Great Post!!