Wait, what?
But LEGO has never made a castle bucket...
Wrong, I say! LEGO has made a castle bucket!
So just what is the castle bucket?
Set #4107

This set was released in 2002, but it was re-released in 2003 under a yellow label (but had the same inventory). It contains 1000 bricks and sold for $20 USD, that's $0.02 a brick!
"But Anthony, this bucket isn't a 'Castle Bucket', its a creator bucket!"
Ahh, yes, but take a look at the inventory:
4107 @ Peeron
4107 @ Bricklink
So what's so good about this bucket?
1) Old Colors
This bucket contains all old colors of light grey, dark grey, and brown.
2) Castley Colors
This bucket contains casltey colors like Light Grey, Dark Grey, Black, Brown, Tan, Green, White and Blue. Yellow and Red are harder, but not impossible, to be used, too.
3) Castley Pieces
1x1s, 1x2s, 1x3s, 1x4s, 2x2s, 2x4s among others.
4) Quantity!
Check out some of these quantities:
48 Black Brick 1 x 1
38 Black Brick 1 x 2
28 Brown Brick 1 x 2
28 Dark Gray Brick 1 x 2
46 Light Gray Brick 1 x 1
30 Light Gray Brick 1 x 2
28 Tan Brick 1 x 1
30 Tan Brick 1 x 2
And that's just a small sample of the quantities of bricks you can get in the #4107 (Castle) Bucket!
5) Price!
C'mon, it's $0.02 a brick! That's incredibly hard to beat anywhere for this quanity and variety of colors.
Sadly, this bucket has been discontinued from the production line. The current bucket offering does not supply the same variety nor quantity of colors and bricks, new colors aside.
But low, there is hope! Yes, friends, this bucket still exists! As it is a bucket, it was never as 'in demand' as other sets, and can still be found, dust-covered behind other sets, or up on the highest shelf!
Run to your local Brick Monger today and see if you can't get your hands on the last remaining Castle Buckets before they go away forever!
--Anthony