I personally would stay in the Concord area. We stayed at the Great Wolf Lodge and had a great time but like you said it's pricey. There are plenty of hotels in that area and since you will be doing mostly things around there that's where I'd stay. Plenty to see, do and eat around there. Plenty of places to stay as well. From my notes there is a Emabssy Suites, a Courtyard, Residence Inn, and Springhill suites all by Marriott, Holiday Inn, Hampton Inn, a Wingate and Sleep Inn at that exit.
Most of the Nascar garages are in the area and are free to get into. We toured Hendrick Racing garage. It was split into two sections. One building housed the current teams and their garges. Across the way was a museum (almost) of past drivers and some merchandise you can buy. Also you can take a tour of the Charolette Motor Speedway. They take you out onto the track and do a loop. It was 9.00 per person and about an 1-1 1/2. You can also sit in the stands and watch the Richard Petty Driving experience go around the track.
Have a great time! Hope some of this helps!