Travelmath provides an online cost calculator to help you determine the cost of driving between cities. You can use this data to figure out a budget for a road trip. The driving calculation is based on the average fuel efficiency of your vehicle, and you can change the gas mileage in mpg or L/100 km to match your exact make and model. Gas prices are automatically estimated based on current fluctuations, and again you can adjust these to fit your local gas station prices. Both U.S. and international units are available to make the calculations easier to use, and the output is given for both one-way and round trip travel routes.
Check the driving distance for your planned route, and see if the total driving time requires an overnight stay. If it's a long trip, you may want to research some hotels along the way. Or compare whether it's better to fly or drive to your destination.