The pricing of the book is "pay what you can". However, I've had issues with people paying so little that, given various fees, the net income for me is $0 (i.e., the only people making money on this are PayPal, Stripe, PayHip, etc).
So, I've configured the payment system to require a minimum payment of $3 (although you can specify any amount above that). If, for some reason, this is too much of a financial burden for you, feel free to contact me.
You can purchase both ePub, Mobi and PDF versions of the book in either letter or A4 format. Once you buy the book, you will be redirected to a page that includes a
zip file that contains all electronic formats.