Asked about in the M'Crack Invasion thread, but I thought I'd start a new thread so that others could find it easily.
There's a Quality Inn in Thornburg, right off the exit from 95, which is about 15 minutes from the site. That's the closest and I hear it's a nice facility, but not a bargain.
If you're looking for a "bargain" and willing to trade 7 minutes of your time for a cheaper hotel, your next best bet is the hotels off of Exit 126, Jefferson Davis Highway, Fredericksburg. There's an EconoLodge, a Days Inn, Ramada Inn and Super 8, I think.
The Econolodge is a dump. I think I would go one exit further out and stay at a hotel at exit 130 before ever staying at the Econolodge again.
The Days Inn is no luxury hotel, although they are renovating, so some rooms are nicer than others, but at about $60 a night, a good deal for the area. The Ramada Inn is a little bit nicer (it's been a year or two since I stayed there) and a little more expensive -- but has more facilities -- pools, bar/restaurant -- than the Days Inn. Which might be nice if you're not onsite from 7am to 9pm like me! Can't speak to the Super 8 or any other facility. There are also nicer (more expensive) hotels on that exit, on the West side, that offer suites. As well as El Charro, a pretty decent Mexican restaurant, in the hotel/south side of the Southpoint Complex and several chain restaurants on the north/Wal-Mart/Lowes side of the Southpoint Complex.
Exit 130 (Plank Road) is another 4-5 miles farther offsite, but you are right near Central Park, home to damn near every chain restaurant and store in the U.S.