That's correct pre-booking the Safari is the best way to go, as sometimes it can get quite busy at the park and depending on your stay there it can be difficult to book a safari. The same thing had happened to some family friends they had to return back home as there was no booking available until 3 days.
Where do I make the safari booking from?
To make a Gir National Park safari booking you need to visit the official site of Gur National Park which is
www.girnationalpark.in/book-gir-lion-safari.html. You will be required to fill in details like the name of the people going to the safari, your contact details, and timings slot you want to go on the safari.
Currently, Gir National Park is closed since 16 June 2017 and will be closed until 15th October 2017. But you can make advance bookings for after 15th October 2017.
How long before should I make the booking?
It is best to make the booking as early as possible to get your required dates. As mentioned the park is closed and will reopen on the 16th October, and as the park is taking advance bookings it would be good if you make your booking now.
The costs for Gir National Park are as follows:
Indian - Rs4900. The cost includes a Jeep which can occupy maximum of 6 people
Foreigner - Rs12400. The cost includes a Jeep which can occupy maximum of 6 people
The costs mentioned above include a jeep and the driver, guide charges, permit charges, camera charges, pick up and drop off from any of the resorts or hotels in the area