At most of our sites we have multiple repeaters and other equipment running from a single (or typically dual) 13.8v supply. One site has over ten repeaters (all 25 watt or less) running this way. But your costs are somewhat exaggerated, and the way we hook them up is different, similar to number 3 on your list.
What you really want to do is provide a "charger" and a battery. The chargers we use are typically Iota type power supplies, usually the 45 or 55 amp variety. They can be purchased for under $200 each, brand new. They connect directly to the battery, and that battery connects through a low voltage disconnect to a distribution panel for the DC to the repeaters. That's basically it. Your battery bank will be the most expensive part, depending on how many batteries you use, but a single 100AH battery would be a start if you only had to hold equipment running for an hour or so (probably longer). Two or three batteries if you wanted to go for a longer time.
As mentioned previously, remote alarms and monitoring would be good, that way you know ahead of time that your charger has failed, and that you are running on DC.
