Replacement Spectra Watermaker Filters

I love my Spectra watermaker, but the filters are really expensive. Today I found a replacement activated charcoal filter. Spectra resells the KX Matrikx Industries brand for $30.50. The filters are nominal 3 micron extruded carbon, 10″ x 2.75″. Filtersfast.com has the same filter (KX Matrikx +10 /2 10-250-190-975) for $8.50.