I need to get to Amsterdam from London. I already have a Eurorail ticket. Is it better to take a cheap flight through easyjet or ryanair to Amsterdam from London? OR, can I get a discount on a Eurostar ticket and from there take a regular train with the Eurorail ticket. Also, how much would the discount be? I have researched every single website that offers cheap flights and I will be paying roughly $70 to $100 to get to Amsterdam. Any other cheap ways? And yes, I've looked into overnight ferrys. They are too expensive.
Looks like the passholder fare from London to Any Belgian Station (ABS) is £50. Go to www.eurostar.com > Travel information > Fares. If you fly Ryanair, you will have a lot of time and money invested just getting to Stansted and then the flight goes to Eindhoven which is a long bus ride to Amsterdam. Or you could fly to Bremen or Düsseldorf in Germany and take the bus and/or train to Amsterdam.
If you take the Eurostar from London to Brussels, you might want to save yourself a pass day and buy a point-to-point ticket for Brussels-Amsterdam rather than using your pass. IC trains are just as fast as Thalys trains for that route and the fare is 36.60 EUR.
Just in case you missed one, here are your budget airline choices for London-Amsterdam: London City on VLM, Gatwick on easyJet, Heathrow on BMI, Luton on easyJet, and Stansted on easyJet.