So I'm going to London next week, and started thinking I should take advantage of its proximity to Paris and take a quick day trip there. There's a tour company offering a trip but it's 14 hours long and that is just too much. I just want to go see the Louvre for a few hours, eat dinner, and come back to London. What the best way to go to Paris briefly?

The darn quickest way to get to Paris from London would be to take the Eurostar. The total travel time gunna be about 2 hours and 15 minutes. The cheapest way might be to fly there.

Is the Eurostar what the call the train that goes through the Channel Tunnel???

The side trip to Paris proved to be too ambitious for this trip, as all the schools were out so the Eurostar was pretty booked up. Hopefully next time we'll make it!

Do you happend to remember how much it would have cost if you did go?

I think it was 147 pounds. But you can check their web site for fare information:
http://www.eurostar.com/

So around $300 or maybe a bit less now...