Actually, air volume IS important for blowing out lines, but pressure is not. 25-40 psi is plenty as long as you can get enough air volume (measured in SCFM, Standard Cubic-Feet/Minute). 2-3 SCFM at 40 psi should do it nicely. Many cheap compressors offer a lot of pressure (psi) but very little volume, so watch out for that.
Lowes has the Porter Cable 6 gallon pancake compressor on sale for $99 this season and is does a nice job on air lines and any size RV tire.
Lowes Porter Cable
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL