If you book well in advance, Eurostar tickets from Paris to London are just €77 round trip. But if you wait until the last minute like yours truly, then it gets much, much more expensive (like, oh, €300). Even easyJet fares were up in the €250 range, which is horrible when you have to get to Roissy-CDG and then into London from Luton.
But thanks to a LOT of surfing around, I found a little back door to cheaper fares: Disneyland!
I was on a site I've used in the past called EuropebyAir.com looking to see if I could scrape together a cheaper flight, and their brilliant search brought up flights AND trains. And lookie here, a Eurostar ticket for just $230 (€175). The catch? The outgoing train leaves from the Disneyland Paris station in Marne La Vallée - Chessy. That's only a 45 minute RER ride from Paris, same as going to the airport. The return trip happily came into Gare du Nord, as usual.
Now if you go on the actual Eurostar website, it's impossible to search for a ticket where you leave from one place and arrive in another. And they really hide that Disneyland Station option, it's buried under "France Stations, under "M". If I had purchased a ticket with them, I would be coming in and out of the Disney station, and on one leg I'd have an hour layover in Lille. So I ended up purchasing the ticket direct from the EuropebyAir site (for those of you with American bank accounts, this is handy since they charge in Dollars).
The Disneyland option seems to be the best for leaving Paris on Sunday night, when fares are highest. If anyone else finds any clever back doors for traveling between London and Paris, do let me know!
(PS: And no, I'm not interested in taking the 10-hour Eurolines bus trip for €69, ugh.)