It appears the EGC2/GC15 batteries are going at Sam's Club for $112.68 these days (Duracell® Golf Car Battery - Group Size 230 - Sam's Club
). I've also found what I believe is a GC25 at Batteries Plus -- can Maine Sail or someone else who knows about these things confirm that this is in fact the Deka GC25? It has a different sort of label, but it's a Duracell brand. GC125 Golf - Utility 6V Battery - Wing Nut Terminal - Duracell SLIGC125 - Batteries Plus
I'm now leaning towards one of these two options. Even if I had to buy the Sam's Club membership, the savings on a single battery vs the price quoted by Rolls would pay for the membership! Thanks again.