The question is whether you could reasonably know that the editing process extended the length of the paper. A factor of two is drastic.
I personally would check (on the web) whether people have complained about such practices of that journal before (i.e. whether it is something they play regularly) or whether the particular structure of your manuscript is especially prone to expand.
If you are a postdoc or a PhD student, you might argue that you expected a certain charge +- some corrections, but that you cannot possibly afford a complete doubling of the cost. As mentioned in the other answer, check that this is not something you could have known before, just to make sure. Nevertheless, if you indeed did not have access to their formatting styles prior to submission, I would consider it questionable practice by the journal if does not permit you to approximately estimate the cost prior to the whole process.
Assuming you could have not reasonably estimated that the page number is going to double, I do not see a problem to ask for a waiver of the difference to the expected cost or, if that's not possible, to withdraw.