I'm another vote for "$600 is way too dear."
If it was really mint, $350-400 would be reasonable in my (rather spendy) market. Also, what most sellers on Craig's List call 'mint' is not even in the same solar system as what I call mint. To me 'mint' is what the bike looks like new, in the bike shop's show room. To some used bike sellers 'mint' means it still has both tires and you can tell what the original color was.
And because I like to share my sickness with others, my recommendation is to spread that $600 over three or four super bargain bikes (I see super deals all the time), ride them around a bunch to find out what your preferences are, then when you find the perfect match, you can resell the others if you don't want to ride them any more.