[garath]

If you are willing to risk non-waterproof for a DRASTICALLY cheaper unit, the Nuvi 200 sells for $154 from newegg.com and you can get some very well made motorcycle mounts for it off of ebay. My father did that for his east coast trip (FL to CT and back again) and was very happy with the results. Batteries for that unit last about 5 hours before needing a charge. But I'm sure you can wire up something if you need longer.