Osmand gives turn-by-turn voice prompts, like any good gps navigation program. You can customize the voice (language). It operates free of wifi or cell service, needing only a gps chip in a tablet. You have to downland offline-usable maps prior to use, and there's a download limit of 10 maps with the free Osmand android version that I use.

Mapswithme will also work, but the free version of Osmand is better than the free version of Mapswithme. The paid version of Mapswithme may be better than Osmand, but I have not tried it. Mapswithme is younger than Osmand but seems to have more development activity and emphasis on improving the user interface, which is a weakness in Osmand (the actual gps location and mapping features are extremely accurate).

I run Osmand on a Hisense Sero 7 Pro tablet, sold exclusively by Walmart. It gives you 95% of the function of a Nexus 7 for a much lower price. I paid $129 for the HS7P and another $40 for 64gb Class 10 sd memory (for camera use), which is $100 less than the cost of a $269 N7 32gb tablet.

My tablet (and most others) will only run ~6 hrs continuously with GPS on, so I use the device intermittently to stretch out battery life. Whenever I see the next turn is an hour away, I note X miles remaining to turn, look at bike computer/odometer and note mileage Y, add X+Y for next turn point, turn off tablet (sleep mode), and when I reach (X+Y-1) miles I turn tablet back on, giving it adequate time (~5 mins) to wake up and reacquire satellites and gps data. You could make a tablet last for 2-3 days in this manner.

BTW, if you're willing to spend the money for a N7, you really should be looking at a Kindle Fire HDX - they were specifically designed and priced to beat the Nexus tablets. Better processor and graphics for $10 less at a given memory spec.