Which castle are you looking for? Is it the 71040, or one of the princess sets? If you're looking for that one, it's $350 through Lego.com. With a little research, though,and some creative decision making, you can whitle that price down some. What I do is go to BrickLink.com, get the parts inventory, then see what price I can get. Sometimes you have to make compromises. Certain bricks are rarer than others, and so you might be better off going with a different color, especially if the pieces in question are structural and aren't visible on the finished build. You can find the instructions for just about any set online. Often, there will be limited edition bricks that aren't necessary, or certificates of authenticity that are costly and ultimately worthless. If you're just interested in building, and not having a particular collector's item, that's usually a pretty good way to go. I'm going to fiddle with it myself to see what kind of price I get.