I've just changed the foam moisturizer and the carbon filter for the first time in 3 years. $40 or something. Don't know if it needed it.What's your yearly maintenance cost? Do you worry about any bio growth in the hose between the first and second stage?
Why would there be bio growth? Clean air and distilled water. The system is not wet; it just puts some small moisture in the air.
Here is the manual.