I was looking at this as well and finally broke down and bought a refurbished Garmin 800 with City Nav maps included for $237. Should be here Friday. It is only a matter of time before someone will build something to interact with the cycle OSM
OpenCycleMap.org - the OpenStreetMap Cycle Map that OSMAnd sounds interesting
The current Garmin Edge's that will do this are:
800, 810, 1000 and Touring