I have already sold a few things that I made with CNC. (not made to order, but made to sell to the general public).
I always try to make sure that after subtracting cost of materials, I get paid pretty well for the minutes that I spend actually making stuff. I do not count minutes spent programming, learning on my mistakes, etc. Just minutes spent to make part X.
Anyhow, this seems to be working out, not too well, but working out. What I will try to do is make a little variety of things to sell, always have one made prior to selling, and making more when the next item sells.
I do not really harbor big illusions, and it will never amount to more than pocket change, but I think that it is a very useful life skill to learn.i