Can the $1 blue fiberglass filters be beat? I was thinking of getting Purolator furnace filter since I had good success with the automotive ones. I cannot find them locally, but on Amazon a dozen are $50. They say they last 3 months, so that is 3 years of filters, minus half for a double return air system and that works out to 18 months. I saw 3M has a 'for life' filter for about $50. You just hose it off with water and if/when it does get punctured you pay $8 to mail it back for replacement.