Affordability is a quality of being inexpensive. Because of the affordability of the apples at the orchard, we went ahead and bought a whole bushel.
The adjective affordability describes things you can afford to pay for because they don't cost too much. People move to certain neighborhoods because of the affordability of housing there, and others decide the affordability of community college makes it a great place to get an education. Sometimes this word is used to mean "cost or price," so someone might say, "The affordability of healthcare these days is just terrible!"