I am looking for a new heater too, but 40 gal. You can download the manual for the Sears heater and look up the anode on Sears Parts direct. Sometimes there is a pic or description of the anode. From what I have read, if it has about a 1/4 dome on the top it is usually magnesium and a flat top is usually aluminum. Both the 9 and 12 year 40 gal Sears look like they have mag anodes, with the 12 yr having a second anode in the hot outlet. This confirms what I saw on the display model in the store. But YMMV, they can change the design including the anode at any time.
Not sure about the pricing, but if you buy online or get online coupons you can save $50 -100 with Sears. If Sears does the install it is possible there could be add-ons when they come to house to bring it up to code.