If you are OK with reading electronically (iPad, computer, PDF etc), I would recommend sticking to the many free sources available online.
The FAA manuals are excellent, and the basics are the same anywhere. Some of the terminology may differ, along with the sequence of instruction, but it will undoubtedly help to gain a good background.
I would also second the recommendation to access the RAF manuals (AP3456). However, to help piece it all together, a couple of sessions of ground school would also be beneficial.
Top tip: you probably don't need to spend more money just yet. Good luck.