How much would it cost to travel from middletown ohio to south carolina by car?

That depends on several things:
Where in South Carolina?
What kind of fuel milege does your car get?
What does fuel cost at the time?
How many people are going?
Is there a hotel stay involved, or will you drive streight thru?

From Middletown OH to Columbia SC it is 560 miles.
at 14 miles per gallon,(a low esitmate) it would take 40 gallons of fuel.
at $2.85 per gallon, that would be $114 for fuel.

Personally, I would set aside $20 per day, per person for food,
and $30 per night for a hotel.
(actually, I would drive streight thru and not stop at a motel, but I drive for a living)

So if its a 2 day trip, for 2 people, using these estimates, cost would be around $225.

Hope that helps a little.