You can download Bondi's "Relativity and common sense", which is written at the high school level, and derives the Lorentz transform using radar based methods and a bit of high-school level algebra. It's an old book and available on the internet archive. I assume that means it's public domain, or it wouldn't be available there, but I don't know how to confirm it's public domain status. You can also read it online, but it's easier to download it and use a pdf reader.any good not that expensive/free ones? I still gotta buy all my books for next semester =\
The material needed for the derivation starts around pg 71-127 or so if you want to get straight to the point.