While lots of my books come from exchanges at laundry rooms & thrift shops, if you are looking for a specific
title, the $.01 + $3.99 shipping at Amazon for used books is more expensive, but you can find just about anything. I have Carol to thank for listing 2 Reacher books I somehow missed; should be here in a little over a week.
Since I'm usually not in one place long enough while on the road to get things shipped, that is part of the reason I spend less while traveling!