Since it is for breakfast, it is all about the time of day you do that in the campground. I find the main value of the inverter is you can run things early without bothering anybody and then recharge the batts later in the day.
Before getting a 31, do read LY's thread on his "Screwy 31" for the extra work keeping that thing going (which he did very well)
One of the guys posted some measurements here a while back on how his single AGM was able to run high amp loads with not much voltage sag so you might find a single AGM will do you just fine
Or maybe look at a single T-1275. (150AH) I really, really like my T-1275s for all sorts of reasons. I now prefer them over my 6s if I had to choose, and I do like my 6s.