You can often find Montana’s for sale on Advrider fairly cheaply, any of the models in the 6×0 series are fine. Differences here: http://www.gpscentral.ca/products/garmin/montanaseriescomparison.html
Mainly the new models have both GPS and GLONASS, a little bit more memory on the newer models and perhaps a camera that you’d likely never use, being that practically everyone has a superior camera in their phone.
Cheap powered cradles readily available. And you know people that can get you the maps you need. 😉
The BMW Navigator is more closely related to the Zumo than the Montana. Neither are terrible.
As for the map pocket… well, cheapest option for sure. Maybe a roll chart is your style? 🙂