Flights and accommodation totaled at about €300 last year.
That was for five nights and with a checked in bag on the flight.
Registration fees might be anywhere from €10 to €50 depending on how many games you reg for.
You'd comfortably make this trip on €600, but it could probably be done for €100 less than that.
Flights could also be gotten cheaper if you're willing to fly Ryanair to London and Easyjet to France, but that's a pain in the hole, so we just went direct with Aer Lingus last year.