Depending on the size of your crew a private charter would be competitive and probably cheaper than what Cape Air is quoting you. If it is even close, private air is the way to go.

Leave on your schedule, no lines, no 2-3 hour check-in before your flight. We took Island Birds a couple weeks ago and since there were only three of us it was somewhat more than the commercial flights, but the convenience and experience was worth every penny. If the price is close it's a no brainier IMO.