All you tight wads out there, I can here you now "$20 for a filter..that's insane!" But, let me tell you (one penny pincher to another), it is worth EVERY PENNY!
Both my son and I have horrible allegies. We both actually should be on allergy shots but I am avoiding that like the plague. Five years ago a poorly supervised nursing student gave me about 100 x the amount of allergen in my shot resulting in some pretty serious problems. But, don't get me started on that one.
Anyway, to keep the pollen count down in our house, I buy Filtrete Maximum Allergen filters. Don't be confused by their other filters, this one filters 93% of allergens while the ones that cost less filter less as well. Basically you get what you pay for.
These filters come in all sizes and the price is surprisingly the same whether you are getting a 14 x 14 inch or 14 x 24 inch filter. These filters REALLY work though! Not only does it help our allergies, as an added plus, I don't have to dust nearly as often:0)