I use a non-aviation Garmin GPS III - the difference is that there's no HSI-like display, and there's no airspace overlay for the map or database of airfields etc. The rest is the same, and it's quite happy with knots and nm. Cost was a third of the price of a Pilot III, probably about £50 on ebay now.
I couple it up to Navbox with no problems, so you just click a few times to define the route and download it to the GPS. No need to fiddle around entering waypoints, although once Navbox has downloaded them once they're in the GPS should you need them.
Of course, I'd like a new colour GPS, but the III does everything I actually need...