A couple comments:

I raised a couple sons. If I were you, I think I'd find some reasonable deal, and then tell him he could keep the difference between that and any better deal he can find. You might be amazed at both his creativity and the effort he puts into the situation. Of course there need to be some guidelines/rules. At least there did for my sons. No hitchhiking, tramp steamers, ??

Gibraltar airport is considered the 5th most dangerous airport in the world, and the most dangerous in Europe. Malaga, Spain (AGP) is only a short bus or train ride away (as mentioned by a previous poster), and Delta has direct flights there from New York (same previous poster thought maybe this was just a summer route).

If you get into Malaga too late for the ground transportation, the Malaga airport hotels appear to be pretty reasonable. I know one can walk from the Holiday Inn to the airport, although it is a little hike.

Romelle