Planespotters.net has a full database on airlines around the world and the airplanes that each owns and operates.
This dataset collects the top 100+ airlines in the world (by the size of their fleet). It is combined with information found on Wikipedia on the respective airline's fleet and the average value/cost of the manufactured airplane.

Updated January 2017.

Dataset includes:

1. Parent Airline: i.e. International Airlines Group (IAG)

2. Airline: i.e. Iberia, Aer Lingus, British Airways…etc. which are owned by IAG

3. Aircraft Type: Manufacturer & Model

4. Current: Quantity of airplanes in Operation

5. Future: Quantity of airplanes on order, from planespotter.net

6. Order: Quantity airplanes on order, from Wikipedia

7. Unit Cost: Average unit cost ($M) of Aircraft Type, as found by Wikipedia and various google searches

8. Total Cost: Current quantity * Unit Cost ($M)

9. Average Age: Average age of "Current" airplanes by "Aircraft Type"

Sources:
Planespotters.net
Wikipedia.org