They have all become pretty standard now. RO
membranes last for about 2 years and the other filters need changing based on use and how yucky your water is to begin with. I'm still using the same unit I got 4 years ago off ebay for $69.99. All the filters are standard sizes and can be replaced at Home Depot or Lowes. DI
resin can be ordered online for pennies and the RO
membrane is standard sized and is easily ordered as well. The name stamped on the unit is what dictates the cost 9 times out of 10.