Arriving by plane

If you would like to travel by airplane the nearest airports to San Casciano in Val di Pesa are Florence's Amerigo Vespucci (code: FLR) about 30 Km away and Pisa's Galileo Galilei (code: PSA) about 70 kilometres away.
Pisa Airport is the main Tuscan airport and is better connected to many EU cities. Bugdet carriers are available both in Florence (Meridiana) and Pisa (Ryanair, easyJet, Tuifly).

Alternatively you can arrive in another Italian airport outside Tuscany. Nearer are those in Emilia-Romagna (Bologna, Modena, Parma, Forlì, Rimini) and the Umbria's one in Perugia.
Regarding cities well connected both by flights, highway and railway to Florence: Rome has two (Fiumicino and Ciampino), Milan area has three (Malpensa, Linate, Orio al Serio Bergamo), Veneto region has Verona, Treviso and Venice.

After you have landed you can rent a car, in all those airports there are several car rental agencies, for the list please consult the official site of each airport.

Car is not necessary to reach San Casciano from those airports, you can get a train to Florence (Firenze Santa Maria Novella station) and then a . Florence's coach station and main railway station are 80 metres far.