I use a cost per mile for comparison...I get about 320 sm in the car for
a fill-up of about $31.50 or a bit over 10 cents/mile. In the cherokee 180
best guess always depends on the winds but let's assume 120 sm (yes, statute
miles -- similar comparisons and such) at 8 gph. I'm paying $3.00/gal
so that's $24/hr or $24/120 sm. which works out to 20 cents/mile.

So it costs double to fly as to drive, assuming straight line.

But what isn't included in here is cost of my time. For example, a day-trip
from Denver to Sante Fe (or Taos) is not practical in a car but
perfectly doable in the cherokee.