Shipping tends to vary depending on your location. I usually pay $5 for mine.
Having said that, sellers usually give you a couple of options! For instance, shipping may be $5 for me, but I don't get tracking or insurance. Plus, it takes about 2-3 weeks to arrive. If you are paying $20, most likely you are getting express mail, tracking, AND insurance. I'm not too sure if you're buying multiple items from the seller either!
So it comes down to personal preference. I prefer cheaper shipping, but of course that changes for every transaction.
I'm glad to hear that you didn't have to pay