I love Prime, but I'm an Amazon junkie. Buy a lot of stuff from them and their sellers.  The free shipping alone is worth the $99 a year.  Some of the things I've purchased would cost a fortune to ship.  With Prime, most of those items are shipped free.  
But if you are only a sporadic user, Prime  may not be worthwhile.  A number of third-party sellers on Amazon may offer free shipping if you're willing to wait sometimes weeks for your order.