That's the going rate.
There was a LONG discussion of this a couple of years ago, either on this board or perhaps SSCA. You might look for that discussion.
IIIRC, bottom line was that it's probably OK to go 1-2 years beyond the battery
replacement date, but not more. After that, you're faced with either ponying up the $300+ for a new battery, or buying
a new EPIRB
Here's one thread: http://ssca.org/DiscBoard/viewtopic....=epirb+battery