Why not spend the investment on a coach/bus station and trying to get National Express to send all of their coaches into Bournemouth via the airport (its hardly far from the A338) and get some of those yellow buses to serve the airport regularly from the surrounding towns and villages.
I think the main problem with the drop off charges is that there is literally no alternative. The airport 'shuttles' are useless and always empty, get some regular buses in there.