How much would it cost to fit and maintain every passenger life jacket with personal beacon?
The extra weight is roughly the weight saved by the introduction of iPads to replace paper. That's apparently saving close to $10K per plane, so you'd expect a similar cost for just flying all those beacons around.

That said, why do you need a full beacon for every vest? If your vests end up scattered over even 10 kilometers distance, you won't have survivors. What you need is a few beacons to locate the plane, and the medium-range active RFID tag on each vest. Such a tag only responds to queries originating nearby. This cuts down dramatically on the battery requirements, as the RFID tag is generally asleep and only woken up by the interrogation signal. Such RFID tags would cost about $20, and weigh a few grams. Battery life is similar (6 years) as that's just chemistry.