Since they are used (however lightly), I'm think 15 each + shipping.
20 shipped for one is within the realm of plausibility, but I don't think many people would go for 5 for $100, unless they were brand spanking new.
...rightful liberty is unobstructed action according to our will within limits drawn around us by the equal rights of others. I do not add 'within the limits of the law,' because law is often but the tyrant's will, and always so when it violates the right of an individual. -- Thomas Jefferson