It seems like you you planned your trip and booked your flights before thinking about the rental car. This is a common mistake, because it assumes that rental cars will always be cheap and available. If this is for a one-way roadtrip, where the car is integral to the experience, such an oversight can turn out to be especially costly. In such a case, as an experienced roadtripper, I always recommend booking the rental car first.

If you plan to pay cash for your rental, try to figure out which way the demand usually flows, or will flow when you get there if during a different season. Then, try to follow it. This usually, but not always, means to start from smaller cities and return to larger ones. A quick check of rates CHS-CLT confirms this is usually cheaper than the reverse, sometimes much cheaper. On the flip side, if you have a bucketload of free days, the best deal is the most expensive direction, opposite demand. As a nice bonus, this often means starting from a choose-your-car large airport (like CLT) and returning to a smaller counter-service one (like CHS).

If you look in another thread, someone was bragging they just did a 9 day cross country drive with Hertz, starting at a Las Vegas neighborhood store, with a medium SUV, for $299. This is probably because, right now, the Northeast has a run on rental cars. Supply is down, and demand is up. Leisure travelers scrambled for one-ways to flee the city into a less restricted region. You'll find photos of quarantined cars with NY and NJ plates against a back wall in TPA and CVG earlier in the pandemic, for instance. Whatever was left was mostly sold off with the downturn in business travel. There is much less inbound one-way demand due to harsh quarantine restrictions for visitors from most of the country.