ACR MicroFix PLB w/ internal GPS from aeromedix.com:
$649.99 - battery good for 5 years

SPOT Messenger from aeromedix.com:
$149.90 - for basic unit
$99.99 - for 1st year of service
$99.99 - for 2nd year of service
$99.99 - for 3rd year of service
$99.99 - for 4th year of service
$99.99 - for 5th year of service
TOTAL: $649.90

At least for the first five years the SPOT Messenger is clearly the lower cost option.
:-)

I haven't been able to determine the cost of replacing a battery on the ACR PLB, but I would hope its much less than $500, so the second five years for the PLB should be even cheaper.

I have an ACR AeroFix from Aeromedix.com, and I feel confident that were I to press those buttons that the device would work right and that help would be on the way.