Many employers & colleges are getting wise to the foundation level maths, which is little short of a joke and don't accept them and are starting to look for grade B as a minimum, ie full GCSE. I don't believe foundation will cover the areas you need to know well enough and it could be a false economy.
I should save your money and do a full GCSE maths, even get some private tuition if you are so keen to get into CTC/CAE etc. Start TODAY as the exam system is about to get tougher from 2015- not before time.
As stated before I think there are better options for your situation.