I can get a AC Delco Group 51 AGM from Amazon for $175 shipped. When I say cheaper, I mean, under $125 USD. Which I don't think will happen. Again, high amp hour AGM batteries are pricey in general. Autocraft Premium from Advanced Auto Parts is $200 (S46B24R) Group 51 Optima Yellow Top is $237 O Reilly's Super Start Platinum AGM S46B24R is $200 I found this chart with common group sizes, then filtered down to stuff of similar size as stock: BCI Group Size L (mm) W (mm) H (mm) L (inches) W (inches) H (inches) 22NF 240 140 227 9 7/16 5 1/2 8 15/16 45 240 140 227 9 7/16 5 1/2 8 15/16 51 238 129 223 9 3/8 5 1/16 8 13/16 51R 238 129 223 9 3/8 5 1/16 8 13/16 52 186 147 210 7 5/16 5 13/16 8 1/4 54 186 154 212 7 5/16 6 1/16 8 3/8 55 218 154 212 8 5/8 6 1/16 8 3/8 S46B24R 235 127 219 9 1/4 5 8 5/8 Unforunately the formatting wasn't saved. Anyway, the Group 22NF and Group 45 would probably fit, but they aren't common either. The 52, 54, and 55 are more common but I'm not sure they'd fit. I'm still looking around for other alternatives but I really do think the Amp Hour rating is what will influence overall cost, and that's probably the most important metric.
The presence of a vent connection is also very important. At various times in the past Advance Auto Parts has popped up a 20% (or even 25%) discount code for order online, pickup at the store purchases. Don't know whether they are still doing that.
If you are a veteran, ask if they give a 10% discount, I know autozone does.... I used it today to get the Bosch plugs.
Yesterday, out of curiosity, I checked the price of that battery at Advance Auto Parts, and today I got an email offering me a 20% savings on order online, pickup at the store purchases. The code is SAVE -- but I don't know whether other people can use it: when I hover over the link, there is a whole bunch of alphanumeric gobledygook, so it may be a unique code linked with my email address.
Good tip still. Maybe any time you start a purchase but don't follow through you will get such an email??