REI, $299, free shipping. Backcountry.com also carries it, same price.

Both the McMurdo Fastfind and the SPOT II have been reviewed on Doug Ritter's "Equipped to Survive" website.

Which one you get depends on what you want it for. All I want is to keep my friends and family off my back by having a reliable source of help should I suffer a serious injury, even though I will probably never use it (an injury at my age would probably end my hiking career, and I don't want that, so I'm extra careful). A PLB uses the military/Coast Guard satellite system which is much more reliable. You also pre-register with the government (NOAA) so they already have your data and don't need to waste time researching your background if you push the button. However, you can't send messages with it. The SPOT II features tracking and "I'm OK" messages to your family. For many people, the tracking feature is the most important item, and they certainly should get the SPOT II. However, since SPOT uses a private satellite network from a company that has had financial problems (Globalstar), it is not considered as reliable if all you want is help in an emergency. It may take longer to get help because Globalstar has to contact the authorities which in turn have to try to trace your family to find out who you are. However, the reviews on the SPOT II indicate that most of the issues raised by the initial version have been resolved. The SPOT II with its annual subscription is more expensive. For a PLB, the initial purchase price covers it all for five years; registration with NOAA is free. Note, however, that if the technology advances as quickly is it has for the past two, the chances you'll keep either gizmo for the full warranty period are probably remote.

Note that per the US Government, the emergency has to be of the life-and-death kind. Water tasting bad or an injury in which you can self-evacuate (such as a sprained ankle) or a sick dog are not life-and-death emergencies. Pushing the button when it's not life-and-death can lead to a heavy fine and free board and room in a federal prison.