Probably the cheapest option is to fly directly via Czech Airlines www.CSA.cz with some offers ranging from 150eur return, or use a low cost carrier like Ryan Air www.RyanAir.com. Ryan Air or Aer Lingus www.AirLingus.com can fly you to Prague from 24 EUR, tax excluded, one way. Another option is to fly to London or Glasgow and then use another low cost airline like Easy Jet or FlyGlobeSpan.