This is one link .
B&B LGW in the gatwick area. We stayed at a place on this road. This road is full of B&B's!
Prices are from £28 a night and there is a bus stop close by that will take to straight to Aviation house and the airport.
It is in a fairly quiet location also with plenty of options for food
at night.
Good luck with the exams. Gatwick is a good venue to take them