Installation isn't the issue. That's so easy it's only worth a buck or two (if that).

OTOH only you can assign a value to the post installation attention to adjusting the release, aligning the cleats, and walking you through getting in and out, plus the comfort factor in knowing (or supposing) that all is good to go. Of course it also depends on how diligent the dealer is, and how knowledgeable your friend is.

Another option may be to lay it all in front of the dealer and see if he'll come down a bit and clinch the deal for you. Not all people - both buyers and dealers - handle this well, so there's no knowing how it'll play out, but you might go back and say you want to give him the business and benefit from the relationship, but can't bring yourself to pay double for that.