I know Aviation Fire has been discussed many times so i am not going to say "Hey i think we should add it", Instead i want to look at the way it would work a bit more in depth.
1: The building
I think it should be separate from a normal fire station rather than just more vehicles at a normal fire station. I think that each station should cost 300K and come with 3 vehicle slots instead of 1, This station type will not increase in price depending on the amount of these stations you get. Prices for expanding airport stations should stay at 30K per vehicle slot due to that the vehicles that you buy are specialist to the airport and would only be able to respond to aviation calls (talked about further down in the post) to stop people from using them as normal fire stations and Airport fire stations tend to be quite large and have alot of bays. For Type 1/2 required jobs these vehicles can be purchased but for a much higher than normal value to once again stop people abusing the Airport station pricing. The building itself will not spawn any calls around it apart from calls spawned by POI, this is to make sure that there is no Brush pile calls on an active runway etc. An ambulance extension will also be available for this station but again again the ambulances will be a much higher price to purchase.
Before i continue please note i am only using the British pictures as an example and most international airports around the world have the same equipment or equipment that serves the same purpose.
Crash Truck: This vehicle is the main aircraft firefighting vehicle, this unit would cost 30K each.
Domestic appliance: This vehicle attends every fire related emergency around the airport and can also respond to medical calls, this unit would cost 50K (due to the balancing situation)
Chief: Attends all medium-large incidents and can also attend medical calls, This unit would cost 10K each.
Tanker: Attends large fires, unit would cost 11,750.
Rescue Stairs: Attends aircraft fires and some medical calls if required, unit costs 15K.
Platform truck: Attends most medium-large incidents, unit costs 10K.