This is my experience of booking to go via Lille, i'll try and explain as best i can.
A couple of years ago i wanted to book to go from Ashford to Disney, this was in February and i wanted to travel in June.
Prices for the direct train were already out and had been for a while so were really high which meant i would have to do the in-direct route.
I rang Eurostar and was told that i could book the first leg there and then and it would cost £34.50 each way so £69 each. I would then have to wait until the TGV prices were released later and book that leg (lille to Disney)separately.
What she did say however is that if i was to wait until the TGV prices were released and then book the whole journey with Eurostar the price would still be £34.50 each way (so £69pp) and that INCLUDED the Lille to Disney leg. I wasnt sure whether to believe her or not and was convinced she must have been wrong but she was actually right.
I did as she said and on the very day the TGV prices were released for my dates i booked with Eurostar for £69 each. Ashford-Lille, tgv from Lille to Marne la vallee and back again.
I have recently been priceing up the Eurostar website for April, now to go from Ashford-Lille on the 30th is £69pp return. However it is still only £69pp to go from Ashford to Disney which includes the TGV leg.
My advice would be to ring Eurostar, find out the exact date when TGV prices will be released and book on that date.
Hope that helps.
