Best Ah/$ ratio AGM Bat for Backup UPS, request for advice...

OK, Have read and searched and cannot quite answer the question. Really apprecaite any and all responses.

I have one dedicated circuit in my home that feeds certain critical things: cordless phone base station, wireless router and cable modem, vonage box, and alarm/smoke system. These things I do not want going down during a tornado or t-storm when I am hunkered in the basement.

For years I ran that circuit with an old APC 1400, but it cooks batteries in about 2.5 years. Found out that it floats the 24v pair of bats (SLA) at 27.6v, which over time eventually causes them to enter thermal runaway and that's the end... After a great deal of trying to "fix" the excessive float, I have decided to but a new inverter/charger.

Probably a Xantrex Prosine 2.0. I know -- overkill for my few items listed above. But I'd like to be prepared for other "contingencies" as well.

The battery will be in the basement in a rather enclosed space, and I am a lazy man, so checking electrolyte will be difficult to assure. Thus my desire for AGM.

I am looking to get one 12, or 2 sixes, and I don't want the bat(s) to weigh more than say 60-65 lbs since the space will require manually positioning the bat and I not as young as I used to be....

I will kill grid power every month or two and allow the inverter to power the loads till the bats are down to about 80% SOC just to verify that they are alive and well.

So these bats will get used rarely, and mostly just float.

I'd like some rec either specifically or generally as to Ah/$ -- I assume that larger bats usually give more Ah per $ right? But since I have an upper level in terms of weight, are there any other considerations? Obviously, I want a good brand as I want these to last as many years as possible.

Thanks in advance....