I have a 500. I say get the 500 unless you are 100% certain, you don't need Cadence or HRM. Then the 200 is a good capable unit. lack of Navigation maps doesn't bother as I always have my Android with offline maps loaded (I have two offline mapping proggies installed, MapswithMe and Sygic) I have yet to use them in a "lost on Bike" context.

I got a grea deal on a used Garmin Edge 705 on Ebay. Check that out. I am more than pleased.

I went with the 800. $450 on ebay for the bundle that comes with HR, cadence, and map card.