Can I do a GSCE in Maths at home cheap?

Hi I'm 23 and am going to start my AAT in accounting soon. At school I did GCSE in Maths but only got a C now back then I really wasn't all that interest in school at all but now I wanna prove to my self I could of done better by re-doing my GCSE in Maths. Is this possible and can I just do it home in my own time. I found a course online but it was like �300 which is really steep was hoping to do it for free. Can anyone help? Thanks