Product review (2 stars): Ouch
I really like the Venta-Sonic humidifier.  However, it requires the use of these replaceable filters.  The filters need to be replaced every 3 to 6 months and are fairly expensive at $17 to $18 each plus shipping.  The biggest concern is that these filters are fairly difficult to find.  My retailer, Bed, Bath and Beyond stopped carrying Venta products and Venta ran out of inventory.  The Venta website really sucks by the way. You cannot even find the filters on their site. You have to really search online to find these.