Having spent 4 years in VT and having flown on a near weekly basis for all 4 of those years, I can almost guarantee that you'll find cheaper flights out of MHT or possibly ALB (2.5-3 hours south on 7 or take the ferry and hit the Northway). I managed to get a cheaper flight out of BTV maybe 5 or 6 times out of 165 outbound flights. MHT also has a few more daily NW flights than BTV.

The drive on 89 is pretty much a straight shot at 75mph (if it's not snowing) and is fairly easy to pull off in 2.5 hours, as I used to do it in slightly less than 2 from Mont-p.