Thy to make it so difficult?
Airplane type have some basic maintenance cost plus a little fee per one aircraft:
737 type maintenance cost: 300,000USD
5x 737/500 - 125,0000
2x 737/800 - 60,000
A320 family maintenance cost: 400,000
5x A319 - 100,000
2x A320 - 50,000
2x A32N - 60,000
for example