Is it permissible to subscribe to a website that offers registration for $60 per month to obtain goods (specifically e-books) for sale, while being unsure whether the books are an additional cost or if their price is included in the subscription?

It is permissible to subscribe to this website under two conditions: that the website is beneficial and useful, and that the monthly paid amount is the price for the subscription. There is no objection if it is the price for both the subscription and the books provided by the website, provided that the books are known to the subscriber, because one of the conditions for selling is that the item sold must be known. If the books are known, then this transaction combines lease (ijara) and sale in a single contract, and this is permissible according to the most apparent of the two opinions of the people of knowledge.