I’d pick somewhere near Malaga, Valencia, Barcelona, Marseilles, Montpellier, Genoa or Rome. Or Sicily if it’s winter. Athens and Dubrovnik would be good options too.

Somewhere with good budget airline options. Barcelona is probably your best bet. Fly from there to wherever there are cheap tickets for a few days at a time. You can get cheap flights from there to all over Europe and North Africa for really cheap on Ryanair, vueling, easy jet,etc.