Hi Sarah,
I'm afraid the main language used is Spanish, although some airlines (such as Vueling) use English. And if your activity is on light aircrafts, you may try the school in Jerez where I think English is also used.
The cost of living is generaly cheaper except housing, which is higher, particularly in Madrid and Barcelona.
But having said that, don't give up: Spanish is not that difficult to learn, especially technical Spanish and you will have such a good life in here.
All the best and good luck
Joaquín