A CR track rental is probably going to be pricey, no matter how you slice it.
Luckily, if you're willing to drive a bit, you've got options!
I'd look at Putnam Park. It's a great track, reasonable prices (Mid Ohio is hugely expensive), but it's west of Indy. Still about the same drive-time as Nelson, and a better track.
You're also going to be relegated to weekdays. Weekends are more expensive and are always scheduled waaaaaay in advance.
If you're willing to drive up to Michigan, there are a couple good tracks up there as well, and dont forget Beaverun in western PA.
So, the list of available tracks:
Mid Ohio: I wouldn't bother asking, we can't afford it)
Nelson Ledges: Do we even know who owns them anymore?
Putnam Park: Great track layout and surface, spartan facilities, probably the best value.
Gingerman: Good prices and availability, but far away.
Waterford Hills: Simple, small, cheap.
Beaverun: Very nice joint, fairly new, gobs of elevation, not sure what prices are anymore.
Bluegrass: Probably expensive, brand new, ambitious project that looks fun as hell.