Product review (5 stars): if you need an MAF2 filter, this is where to get it
If you need a MAF2 filter, it's hard to find in box retail stores, and the price is reasonable.  The inherent problem with these is that they soak in water and eventually rot away.  You have to replace this filter for every winter, maybe more than once.  I've always wondered if it's worth having a humidifier with a filter that you have to repeatedly replace.