Price is 'fair'... I paid $24500 for mine with 62k on it 4yrs ago (90% condition, bald tires, Big Horn Package). And for my area, I got a really good deal.
If it is a decently optioned truck, get it. The 4spd auto sucks for towing (if this has one). The gears are just too far apart. I'm running an Edge Juice, and my dad has an '01 Cummins (6spd manual, 3.55 gears, Edge Ez). I easily exceed his horsepower/torque output even on my stock flywheel output, but the 2 extra gears allowing each one to be closer makes a big difference. Where he would drop to 5th, I would have to go to 3rd and rev harder... The lack of gears sucks.
Mileage is great, and the 03-04 models do not have the 3rd injection event (emissions related), so they will squeeze a tiny bit better fuel economy than the 04.5-07 years.
Common issues are injector failure (install an aftermarket 2-micron fuel filter), super sloppy 47/48RE transmission (install a TransGo SK48RE shift kit.
Go get you a Smarty Jr programmer, run it mid-level without added timing, and make a good amount of power with reasonable exhaust temperatures, and go gross 25k pounds if you want. You're going to be limited to the tire capacity. Stock 17" tires will most likely have 3195lb ratings. IIRC my rear axle is rated for 6064lbs, 9k GVWR. Your GVWR will be a little higher.
I'd talk the guy down a few thousand and get it, if it is what you want. Compare price to others listed in your area. Because of the low mileage, I expect 'your' truck to be near the top of the spectrum. I love my 05, and plan to keep it for a VERY LONG time.
2003 S.O. Federal Emissions: 250HP/460lb.ft. Available with NV4500 or 47RE
2003 S.O. Calif. Emissions: 235HP/460lb.ft. Available with NV4500 or 47RE
2003 H.O. Federal Emissions: 305HP/555lb.ft. Only available with NV5600
2003.5 The 47RE was replaced by the 48RE automatic transmission and now available with the H.O.
2004 S.O. Calif. Emissions: 235HP/460lb.ft. Available with NV4500 or 48RE
2004 H.O. Federal Emissions: 305HP/555lb.ft. Available with either NV5600 or 48RE