You have a problem straight away with MYW on a 3 week trip, they are only valid for 14 days from 1st use.
You can buy a 10 MYW, Hopping, Waterparks & DQ but its $394.05 (£240)
A UK 14 day ticket would be £219 (although there has just been an offer on to get them for £198)
IMO the best value is the 21 day Ultimate ticket at £250, unlimited admission to everything for the whole 3 weeks.
Depending on time of year you go there could be a free dining offer on, then you would have to buy the UK tickets (for UK deal)
All this years prices, next year will be more.