Sorry Ron but last time I was shopping for batteries it wasn't even close.

My boat uses 4 group-24's in the house bank, another group 24 in the bow for the windlass and thruster, and another group 24 for starting. Let's say I only want to replace the 4 house batteries. Lifeline AGM at Defender is currently $330 each, or (x4) $1320. I found Optima Blue top online 75AH for $239, or x4=956. Defender Sportsman flooded deep cycle Grp 24's (90AH) are $90 each or $360. If I go to my local Costco they are $60 each x4 = $240. The Costco batteries are are discounted by the "core rebate" when purchased if I bring my old batteries, are rated 85AH and come with a 5-year warranty which will be honored with no questions at any Costco if needed, whereas if you purchase from any source that doesn't have a local retail presence you can't benefit from core or warranty unless you ship it (doesn't pay, especially if you need it now).

So while AGM is clearly better technology, I think it's also pretty clear you pay a big premium for the benefits. I could replace my Costco Kirkland house-brand batteries 4 times before they'd come close to the cost of AGM.