With that many of you, I suggest your group get in two taxis and head over to the municipal airport and catch your flight from there. The airfare is $120 US from International, but only $67 US from Municipal. The taxi costs $25 US. That is two taxis x two trips (arriving/departing) = $100 to split between eight of you. That is only $12.50 each for the taxi rides. You will save $53 each on airfare, minus the cost of the taxi, for a total savings of $40.50 each. That is a savings of $324 for the group of eight.
Make sure your arriving flight at International lands early enough for you to get through baggage/customs lines and take the 30 minute taxi ride over to Municipal in time for their last flight of the day over to SP (which, according to their website today is at 5:30 p.m. daily). I would also ensure your seats on the flight by booking ahead of time online. Their website is www.tropicair.com.
That may not seem like much, but $40 extra bucks in your pocket will buy a few meals or several Belikins!