Ditch any touch screen! The UI is terrible. Get him something with buttons.
Like the Garmin 276cX, smallest chart plotter. Dedicated buttons to zoom, pan, drop a pin. Don't pay for Garmin's lame base map, compile and download the OpenSource base map and put it on a small card in the back. Just be sure to format the card in 16 bit.
This is the more expensive solution, maybe $450-550, but it will out last most of us seniors. Once you've tried the zoom and pan on this unit, you'll be hooked. That all said, the biggest advantage is you can zoom out 5x beyond any touch screen and still see all the elements of a map. It doesn't drop out map details until zoomed way, way out.