Harbor freight has on sale a portable air compressor. Its performance is comparable to the Viair 300P series.
300P12-Volt
• Permanent Magnetic Motor
• Duty Cycle: 33% @ 100 PSI
• Max. Working Pressure: 150 PSI
• Amp Draw: 28 Amps
• Min. Ambient Temp: -40 °F
• Max. Ambient Temp: 158 °F
• Dimensions: 9.80” L x 4.90” W x 7.50” H
• Net Weight: 8.60 lbs.
300P Performance Data: 0PSI @ 2.40CFM, 40PSI @ 1.48CFM, 70PSI @ 1.13 CFM, 90PSI @ 0.92CFM
HF9318612 volt motor, 30 amp, 150 PSI max.
Air delivery: 1.35 CFM @ 40 PSI, 1.14 CFM @ 70 PSI, 1.05 CFM @ 90 PSI
Overall dimensions: 11-1/4'' L x 5-1/2'' W x 7-1/2'' H, Overall weight: 11 lbs.
Sale at under $50. There were plenty of write-ups for similar acs in the past.
http://www.gearinstalls.com/pepboys.htmhttp://www.4x4wire.com/tech/portable_oba/Add a small tank (~$50), an air plenum (~$15), hoses, switches, wiring (~$30) and get on-board air source rather cheap. it won't quite be a source for air tools to repair an axle, but you could use the air tank as the source for using air tools in a timely fashion. No more driving couple miles to air back up your tires. While you are reconnecting the sway bar, respooling the winch cable, etc. you could be airing up your tires.