Airport hotel for Mumbai

Hi, I am travelling with my family (wife and 10 month old baby) to Seychelles and my flight is from Mumbai at 4am. Since I’ll be flying in from Kolkata and reaching Mumbai at 10pm I wanted to know if the airport hotel at the Mumbai terminal is a good option to relax and stretch our legs. How much does the transit hotel cost? Should I pre-book it or walk in and get a booking?