This should neither use a large amount of mobile data nor use as much battery as Gmaps. Can't speak for iOS but this is what the Android documentation below has to say on location strategies and what it boils down to is that you need to determine how much accuracy your app needs, pick your strategy and maybe implement it as a background service that talks to your app. Someone who coded for Android before should have a prototype up and running within a few days. I assume however that this involves extensive testing on various devices and OS versions (the tricky part of mobile development).

http://developer.android.com/guide/topics/location/strategies.html