I'm trying to go to Paris for a day and a half while I'm in London for 9 days....I looked at flights yesterday and they were all $240 or so, and are now much higher...Train tickets on Eurostar seem even more expensive!

Any advice on how to do a quick trip to Paris, and the easiest/cheapest way to do it? Also, are the airports directly in Paris, or out of the city? I'm trying to figure out if it is better to fly or take the train, and any tips on finding discounted rates-I know there are sometimes discounts for people under 25.

Thanks for your help!!