I have an Amazon Prime membership and I can invite up to 4 people to "share" the membership with me. You get unlimited, Free 2 day shipping, you can upgrade anything to 1 day shipping for 3.99, and on select video games, movies, books, etc you get free release day shipping.
I pay $80 a year, so i'd only ask for $15 per person (via paypal) if you are interested. PM me if you are interested and i'll send you an invite.