If you're a good salesman you can expect to get your logo's purchased at $500+. It's quite easy, honestly. You just have to be honest and tell them straight forward, it's not just the design itself, it's the time you spent on the labor to create it. Even if it took a few minutes or so, still, it's the labor and the customization. Also say you include unlimited revisions till satisfied and will make any minor adjustments anytime they need. To them, that logo is personal to their business and will last years, hopefully. That logo will represent them for the long term and if they are happy about the work, they will invest in happiness.