A refurbished and Garmin-warranteed 705 is about $340 with the speed and cadence kit, another $100 for the maps to make the GPS useable. The electropak is what - about $180 and you'd have to add to that whatever your mapping device costs.

As much as I've complained that Garmin's documentation isn't up to snuff, the device itself is very nice and there is a lot of information on BF and youtube about how to get the most out of it.