Mexican vanillas are strong as they contain both natural and artificial vanilla flavors. Alcohol content is about 1/3 of US product. Prices are cheap, we see it in WalMart for under $7 for a 1 lt bottle.
Put a fine a perfume sprayer or some other fine mist sprayer with undiluted mexican vanilla and spray the filter media with 8-12 squirts of vanilla. Instant AROMA.
Course it doesn't last and will need to be refreshed a couple of times a day.
But compared to the things that hang on the filter, this is LOTS cheaper, even if it means more work. And vanilla is a great scent around the house/apartment.