Amazon has Fisher Price Trios on sale and currently you can save an additional $10 when you buy $25 worth of Trio items shipped from Amazon. Enter code TRIOSAVE.
My son got several sets for his 6th birthday and both he and his 4 year old brother really enjoy them.
We have the King's Gatehouse (now $9.99 instead of $24.99)
We also have the Hammerpult ($14.99)
And the Siege Tower ($9.58 instead of $14.99)
EDITED TO ADD:
Just saw they reduced the price of the Castle (which my son has asked for repeatedly!) to $34.09 instead $74.99!