Unfortunately, I think you will be paying through the nose for any lodging in Austin that week - if you can find anything. You might also consider looking for motels up north like Roundrock, Georgetown and Leander but those are all in the metro area and likely to end up in your initial search.
In case you're not aware, the only two shuttle drops are downtown and the Travis County Exposition Center (east side of Austin, north of the track). Be prepared for long bus lines at the end of each day and things to not run smoothly. This is the first event and there's bound to be hiccups. It will all be worthwhile though. Can't wait!
But maybe you have a premium ticket with a parking pass.