I've been stalking the Sear's website for the best price on this battery, and it changes every single day for the past two months. This is definitely the lowest price I've seen for this model:
http://www.sears.com/diehard-marine-battery-platinum-pm-1-group-size-31m/p-02850131000P
Better jump on it today though, because I guarantee you it'll be back to $260+ tomorrow!