Hire a nine seater Tempo Traveller, which you should get for about 24 Rs. per km for 300 kms per day.
U should take 8-9 seater car that's also available in Rajkot and it will available at nearly 13 rs per km.
8th u should go to dwarka
9th u can visit beyt dwarka and nageshvar temple
10th leave for somnath
11th leave early morning from somnath so u can reach rajkot @ 12 pm (200 km 4:30 hr)
A car like Toofan will work out for you and will be cheaper but not as comfortable as Tempo Traveller.