Legoland is apparently not enough of an attraction to make it viable. Reasonably priced flights via Amsterdam though (not cheap mind), or Ryanair via Stansted.
Fly to Copenhagen, rent a car or take public transport and time your trip so you can have a day in Tivoli Gardens as well. You can fly to CPH for less than a €100, remember to check SAS not just Aer Lingus and Ryanair.