Use d bahn to research the rail options, and skyscanner to research the flight options. Keep in mind that England is an hour behind the continent so you'll "gain" an hour on the way and "lose" it returning.
Option 1 takes about 3 1/2 hours from CDG to St. Pancras, using RER to Nord and allowing for the 30-minute advance check-in for the Eurostar. You might want to book on a later Eurostar to build in a cushion for flight delays, airport delays, RER and Nord delays.
Option 2 works if you get the TGV at 10:06 from CDG to Lille, then a half-hour connection to Eurostar, arriving St. Pancras 11:30, total about 2 1/2 hours. The 10:06 departure allows you about 3 1/2 hours after landing, which ought to be enough for baggage, border control, etc. as long as the flight isn't very late.
I didn't research Option 3 but there must be very frequent flights between CDG and Heathrow or Gatwick. Build in enough time for bags, border control, possibly changing terminals at CDG, and of course transfer from the London airport to the city itself. I doubt if this all could be done faster than Option 2.
I didn't try to calculate costs for you, surely you can do this yourself. Note that these advance purchases are non-refundable and may be non-changeable too. So build in some time for contingencies. Scenery is significant with either rail option and zero with the flight.