Last time when I turned my car in for maintenance, it cost me 15k, with air filter, oil filter, cabin filter, Total oil.
Also got the cabin filter AKA A/C filter changed because the old one had gone beyond the stage of cleaning. However, after that, I noticed I didn't get influenza as frequently as I used to. All thanks to the clean air pouring into the cabin. Cooling significantly improved as well.
Just a thought, may help others.