Yes eBay rates are usually cheaper then self shipping and some options are not always available. If you’re shipping a calendar or other printed materials or things like cds, check out USPS media mail. Those rates are often ridiculously cheap imho.
Media mail isn't a bargain any more, Depending on size and weight, it is often more expensive than ground advantage. Plus, any media mail package is subject to postal inspection. I have had that happen to me, a package containing a set of CDs arrived ripped open and retaped so you could see the contents, even though CDs are allowed in media mail. Also, media mail packages can sometimes take much longer than normal for delivery.