You may contact European Airlines to find better prices

If you are going to one more cities, European Airlines like Lufthansa or Air France may also provide the same price but better service, they charge the same fare if your arrival and departure cities are different, and provide some route free by stop over so that you can save $$ of train cost.

For instance, the Air france price from MIA to CDG from 9/11-9/25 is just $360,the same price offer to MIA-CDG-NCE. And no doubt Air France provide much better service than UA.

Call them to find if there is good deal.

If you do return from CDG, suggest you spend 2-3 days visiting chateaus in west France and Normandy area.