I was at Costco yesterday, and on the way out I dropped into their tire shop and checked out the battery rack. My Interstate Workhorses are nearly 10 years old and the house bank showed some signs this fall of not being up to their old snuff. The two chassis bats never failed to be at the ready, regardless of warm engine or not.
They no longer carry Kirkland-branded batteries; they are all Interstate. The largest duty chassis start one is 850 cold cranking amps (Group 65) for $90.
The 6 volt Golf Cart battery is $84. There is of course a $15 core add-on to that price, but I'd be taking in my old ones to immediately get that credit back off the top.
Recalling the much higher prices I was quoted at various other facilities this fall for similar batteries or Trojans, I know where to go now when the time comes, given there is also factored in a Costco Executive (and/or other) member kickback later. If I put that in the mix, I calculate my net cost for 2 chassis and 4 house batteries to be $500.46, depending on the exact kickback ultimately given; but regardless, the net cost will be not much more than that, if not that.
-Joel