As someone who grew up in the area (Dillon) and actually worked at South of the Border during the summer while I was in high school, I would suggest that you look at South of the Border for what it really is: a large truck stop/rest area. In fact, it is ranked number 10 on the Travel Channels world's best truck stop list.
There are other hotels/motels at the next exit in South Carolina (Hampton Inn, Comfort Inn, Ramada Limited), but remember you get what you pay for. Rates at these hotels/motels and South of the Border are cheap for a reason. This is a small southern town. It is rural and agricultural.
Florence, SC does offer some better options. I would suggest staying somewhere with Marriot in the name. As for the room, you will know what you are getting.
Lumberton, NC may offer a few better options than Dillon. It's about 20 miles before South of the Border and it's a little bigger than the Dillon area, but not as big as Florence. Fayetteville, NC is about 40 miles before South of the Border and I would say is your best option for staying in that area.
As Sleepy posted, if it's a race weekend, forget about finding a room anywhere in the area.