Try this like for Interstate Batteries in CC. The big battery for MB should be around $100. I've been using them in all my vechiles for years. MT-49 or MTP-93 (biggest)
http://www.ibsa.com/estore/dealer_locator_results.asp?mscssid=QXADT4J4XPM79NEX1DD873T5AFWACFV0&js=1