Some guesses based on other ACR models. Probably $300, which will include a new battery, new case gasket
and testing. (Supposedly.)
If that model comes apart with 4 stainless screws or similar, then it can be opened up and a web search probably will find you the battery type for $75. Most of them just unplug and replace, some have to be assembled in packs, some are actually potted in place. The gasket
is usually an o-ring or other dollar part, and if it is not distorted a little silicone grease and cleaning
are all it needs, then retorquing the case carefully so it is watertight again.
The other school
of thought is that this is incredibly dangerous, almost as dangerous as lighting
fires in your house in order to cook your own dinner. (Hey, some people are better off calling for reservations.(G)
Yes, it may be critical life saving equipment
. But the job is more like changing flashlight batteries in a very high end flashlight, not brain surgery.