Getting some one to do it "on the side" is poor practice as he is
probably not licensed or insured. Also he may be using school district
tools and materials, you could both be in trouble with the law if he
gets caught. If he wants to be a contractor he should do it full time
and not get subsidized by the school district.

The price seems fair, not having seen the job. The VS motor and two
stage makes, higher efficiency furnace would be better (90%). Since
you are in upstate NY, heating efficiency will be more important than
cooling efficiency, but I would have gone for 11 or 12 SEER anyway.

Stretch