Very good point - I hadn't thought of buying used for that purpose. I usually just head over to iTunes.
When I insert a cd into my computer, iTunes automatically uploads it and puts it into my library, so no need to convert.
What I started doing was instead of buying an entire album of an artist, I check out the top 5 songs. Typically they are the best and the only ones I want anyways... then I buy those singly off the different albums. So I get by with only spending about $5 instead of 10-12.