It sounds like you are tighed up in knots:
First of all, please don't lose this dream home for a few thou; you are talking $10-$20 per month.
You are buying a HOME first, and an investment second: In a few years, you won't care what you paid.
If you are not in a multiple-offer situation, you may get it for $105 and you shouldn't have to worry about the Appraisal. If you offer more than that, you would have to pay the difference, and if you offer less, you may not get it.
Don't worry about New Const vs Old Const; the Appraiser allowed for this in the appraisal: He worked with what he had. Comps are Comps.
Good luck and may God bless