An FAA type rating isn't going to be much use to you in a JAA airline. In any case, EZ and Ryanair's requirement is for type rated and experienced pilots on the 737 for direct entry commands and accelerated promotion.
In general, a type rating alone isn't worth the money. Most airlines in the UK will want to put you through their full training system, whatever your previous experience, and will give little or no credit for a type rating with no associated line experience.