Originally Posted by hdogan

You should be fine - https://www.hertz.hr/en/generaltermsconditions

"Cross border fee of EUR 7 daily with maximum charge of EUR 21 applies for driving the rented vehicle across any Croatian border with the exception of the Croatia – Bosnia & Herzegovina borders on the A8 main road (route E65) between Split and Dubrovnik, with the crossing allowance of maximum 2 hours in Bosnia & Herzegovina."

So, 7 Euros a day, unless you're just driving thru B&H to get to/from Dubrovnik, when it's free.