According to the opening post he wants to save money.
He can only save money if he is not buying the proper course material... and that might cost him more in the end due to failed exams, so it's probably not saving him money but costing him more money anyways.
If it's just about some pre-study about the flight characteristics and meteorology: sure, any material will do. But then he should not bring it as a cost reduction, but as an extra investment on top of the proper course material of which most will be redundant, except for some details (and the AirLaw).
In any case, it's not necessary to do any pre-study anyway, and most relevant basic information will be given by the instructor in the first few lessons. It's even on wikipedia. What makes a plane fly, what are the controls, how is lift generated, what are clouds, etc. No need to buy anything.