The UK's "exit tax" which can be very high may figure into your decision on whether to fly out of the UK back to the US or return via somewhere else in Europe that doesn't impose these very high fees on travelers. I've done many a DEN-LHR - Eurostar - CDG-ORD-DEN trip with my family of five and put the saved money towards some fun in Paris

EDIT: Avoid EWR at all costs.

EDIT2: A dummy booking in Premium Economy 11/22 to 12/6 flying into and out of the UK priced at $1589 of which $290 was exit fees. CDG exit fees re about $40