Trekker comes with the PDA it needs to work, which is to say it's all
self-contained, for all intents and purposes. 

The most inexpensive solution thus far (and by no means perfect) is:

A Series 60 mobile phone on a GSM network (Nokia 6682 was the most
recently discontinued, although new series 60 phones are coming). Add
to this either Talks or Mobilespeak and the free GPS software
Loadstone (www.loadstone-gps.com) and a bluetooth GPS receiver. Let's
see. I've seen Mobilspeak at $200 for a limited time, but think closer
to $300. Then the cost of the mobile phone. $100 give or take $20 for
a bluetooth GPS receiver. 

While this is less expensive than Trekker, the maps with points of
interest are far from as complete as those that ship with Trekker or
Braillenote GPS, containing only street intersections and, generally,
no businesses or address information.
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