"Birdlives" I don't know if you left already but here is a website for a company in the Netherlands that rents sail-boats. You mentioned Amsterdam. Be advised that within 1-1/2 hr travel from Amsterdam you could reach 90% of the available water and besides this one there are more companies. Although this is on the largest body of water besides the North Sea/Atlantic. ($1,000 to $1,450 US/week for the range of boat you're looking for)
zeilboot huren, zeiljacht huren ijsselmeer, Andijk zeiljacht verhuur
let me know if I can help sometimes their web site doesn't convert to english but you can always e-mail them.
s/v "SAILMATES" 1973 IRWIN 32 Classic