In both the UK and the USA you are not allowed to pay for a written review of your book unless the writer specifically declares they have been paid to write it. This means that you will be banned from putting a review on Amazon as it is against their rules.
However you can pay for a persons time and it will take most people 7 – 10 hours to read the average book, about 100,000 words.
Beta reading is slightly different, you are asking someone to read your book before it is published. You should make sure you agree what you want from a beta reader before you start. Is it just about pace, plot, and characters? Do you want a formal report and the minimum length?
If you would like me to review your book you can contact me through Fiverr.