Might I ask what environment you have the machine in? stable temp or wide variations? Humid or dry? My Nomad is a wet basement, and I spend about $30 to $40/month during the worst of the year to run the dehumidifier as primary protection for several machines and way too many other tools (as well as several other protective measures).
I ask because, if your environment is less controlled, there are a number of ways to prevent rust formation. Two easy ones are: a) a small heater, like those sold for firearms storage, in the machine to keep the temperature a few degrees above ambient, and therefore at a lower humidity; 2) remove the collet and nut when not in use (they should be loosened when not in use, anyway) and roll a small piece of VCI paper (vapour phase corrosion inhibitor) into a tube and slip it into the spindle bore, then put a plastic cap, like a pipe thread protector cap, over it. VCI materials leave no residue. ALL of my tool storage gets regular replacements of VCI capsules or paper, but my Nomad has not needed it, to this point.
Also, if you machine wood, clean the machine of chips and dust thoroughly after use. The wood chips and dust may hold moisture in the enclosure. I have seen this with woodworking machinery a few times.