Learning to fly cannot be done cheap.
You only need a few books costing around £120 in total to get your basic PPL. As a percentage of what you will pay to pass, this is a very minimal cost so why try to cut corners here ?
Get the books and study them hard. If you learn what you need and learn it well, such as navigation and track error, etc, this is more likely to save you money in wasted lessons while you try to understand exactly what it is you are doing.
I used to "learn the stuff" then try it out in the air with the instructor and it didn't do me any harm.
One other point is that the books are being updated all the time. There may only be subtle changes but it is better to have the most up to date information as this is what will be in the exams that you take.