Was thinking the same thing. A colleague of mine used to leave the car @ COS long-term airport parking for 1-3 weeks all the time. She also used to do "mini-leases" through hertz which, though not sure they still exist, worked out to about $10-15/day and parking @ Hertz lot was free (including a wash).

@ $5/day (30day max) I think Pike's peak is the best you'll find without "bending" a rule or two.