you may (or not) find significant savings by flying to LHR (London), and then making your way to Amersfoort on a second set of tickets (eg. British Midland cost me CDN$220 after taxes return LHR<-->AMS), or possibly via Cambridge..

Or even one of the cheap no-frills airlines (it's only a 45 minute flight after all) - EasyJet flies from London Luton (closest to Cambridge) to Amsterdam.