you also have to take into account for the controller aspect of the cancel button, if you make an 'x' close button they would still have the option of accidentally closing it.

Instead why not have a button combo? for controller players you have to push both the square and triangle button (PS3 controller); this is the most unnatural simultaneous button finger placement. On keyboard/mouse configurations use the 'esc' key? I mean you don't really ever need to have you hand over in that area when crafting anyway (since you'd be using the arrow keys to select your synthesis options) and if you are mainly using the mouse you never have to worry about hitting it on accident since there is no on screen "quit" button (but I assume if you have a mouse you have a keyboard, but if you have a keyboard you don't necessarily have a mouse).

That's how I would do it anyway.