Good morning Jennifer! I've beren buying Shell Rotella 40wt from Jamestown Distributors. I have ordered oil twice from them at 6 gallons per order to refill my oil resevoir as needed. Per gallon it costs about $22 plus shipping, which is quite expensive because of the weight. They sell a 55 gallon drum for $715, but I can't even imagine the freight charge on that. Here's their link:
http://www.jamestowndistributors.com...t.do?pid=8423#
I'm sure you can call them and get a quote. My mechanic found a local source here in Southern California for 55 gallon drums, but I don't know what he paid for it.