Before Covid you could do this, now all the archeological sites require you to have an accredited guide for you to be able to enter. It's cheaper to book a guide full time to visit multiple sites in a day than it is to book one to go to each site one at a time. As always, if you want something other than the 'on rails' tour they can do in their sleep, like extra time at some sites, then make sure you agree it with them first before signing on the dotted line. There are plenty of places you can go without a guide like the beach and hills, but not any of the places you go there to see. So I would no longer recommend hiring your own car.