When looking at one way rentals, there are basic guidelines you can use to get the cheapest rate possible for a one-way car:

1. Do a lot of comparison shopping.

Check multiple companies for availability and rates and check multiple locations within the same city (airport vs neighborhood location, if that is something that you are able to do), for the city, pick up and return dates and times and the car size that you're looking for.

Check rates using a discount code, if you qualify. There are hundreds of membership programs and professional associations that offer car rental discount codes to their members. You can find a list of over discount codes for 8 major car rental companies, right on this site.

2. Take the smallest size vehicle that you would be comfortable with.

You'll not only save money on the rate of a smaller car, but you will save money on the gas, as well.

3. Keep the one-way car as few days as possible.

The rate for a one-way car rental is higher for each day. The sooner you drop off the car in Atlanta, the less days, the cheaper the rate. If you need a car while in Charleston, it is usually cheaper to rent a seperate vehicle for the remainder of your rental.