I'm hearing around $900 per door. No confirmation on that yet though.
You can modify your current doors for about $50 (for the PAIR) in a couple of hours. You will need a jig saw, hand drill, a couple of pieces of 0.10" Plexiglas (same as the current window), a bag of screws/nuts/washers, and a tube of RTV.
When you take the interior trim off the door, the cut pattern is obvious. Either leave a margin of about 3/4" from the stiffener for a frame, or (for the most view) drill out the rivets, put the Plexiglas between the skin and the stiffener and install new rivets or screws. The RTV is to seal between the skin and new window, both to stop leaks and to prevent vibration.
You can buy a spare set of doors for $100 - $175 per door, and have a spare set to swap with the original doors, for a total parts cost of $250 - $400 for the pair.