I know how you feel- my maths coursework is due in four days too, and our teacher hasn't given us any indication as to what roughly should be included (by that I don't mean the actual formulae; I'm just not entirely sure as to how far we really need to investigate, and what stages this would involve).
However, even if you don't plan on copying it word for word- you said yourself that the formulae you need are included; therefore I assume this means you want to use them from there. Even if you do explain them yourself after looking at them, you will have cheated in copying the formulae. Part of the marks come from determining patterns yourself.
I know it's tempting, but rather than spending your money on something which could land you in trouble, as these coursework sites often do work together with the exam boards (CN mentioned it on here a few weeks back), and they have the means to attempt to find out if work has been plagiarised; it might be better to speak to your teacher and explain the situation. If you are completely unsure as to how to continue, then I'm sure (s)he will be willing to offer you some guidance. You could also talk to other people in your maths group, as they will be doing the same coursework as you I presume.