From things I've been reading on FT and elsewhere, I'm hearing that loads are way down for Europe over the summer. I'm expecting there to be sales coming up when they decide it's time to get some butts in those seats.
Also, it has been a while...(okay a good long while

) since I've used STA, but I remember them being very good, and never used them for groups or package deals. One trick is to ask them for advice.
for example: NYC-CDG may be $750, even for students, while BA will be offering a student price to LHR for $375.
Then you can look at the European LCCs.