Your first bet would be to check out industry periodicals. While, many magazine are losing money, most publishing magazines are still in business. They are staying afloat. I am talking industry magazines such as Library Journal, Publisher's Weekly, etc. They pay to review books but it is not alot $25 per review if even that. You do not get paid by the word, or for your time reading. You will get the ARC of the book.
Most of these periodicals, and consequently their online counterparts, will require that you have some sort of background to qualify you to review for them. Most of the reviwers are either current and former librarians, teachers, professors, former editors, former author's etc.
Hope that helps