Like the other guy said, only difference maintenance-wise
between a 172 and a 182 is the prop, governer, horizontal
stabilizer trim jackscrews (for the early ones) and fuel bladders.
If we are talking point A to point B cross country trips, I think
that from a fuel efficiency stand-point, you will find that the 172
and 182 are awefully close (the 172 will probably be a little more
fuel efficient). The 172 burns less fuel, but takes longer to get there.
I did a comparison with my old C-170B and my current early 180,
and the 170 was slightly more fuel efficient on a cross country
trip. Factor in the extra load-carrying capability of the 180,
and the higher cross country speeds, and it doesn't take
much to justify the slightly higher operating cost of owning
the 180 vs the 170. I just wish I could afford to own both...
200nm trip
C-170; 100 knots @ 8gph = 16 gallons (@ $5.00/gallon = $80.00) for 2 hours of flight, nmpg = 12.5 nmpg (14 smpg)
C-180; 130 knots @ 12gph = 18.46 gallons (@ $5.00/gallon = $92.30) for 1.54 hours of flight = 10.83 nmpg (12.13 smpg)
I'll also agree that a cheap airplane (172 or 182) isn't always
the best airplane... That being said, a friend bought an early
182 for about the same money (mid-20s) several years ago.
It had (still has) a run-out motor, bad paint + worn interior,
but the airframe is "arrow-straight" + corrosion-free (he seems
to have fun with it just as it is...).