When I bought the Phat shower filter, I contacted the seller through eBay to ask about the running cost. With filters, the running cost is more important than the initial cost.
He said to me that the replacemnet cost was $65 and if I become a member, I could get it for $45
After I bought it, I asked where this membership was and was told to txt his mobile number. Over the course of 2 years, I wasn't able to get that price once and he was very rude to me when questioning. I finally threw it out and bought a new one.