Nelsons is my first track (many years ago). Backstraight is a lot of fun. I have been told that the repave improved things quite a bit and I haven't talked to anyone that wouldn't go back since driving it since the repave. I haven't run there since the repave but plan to, time permitting.
Cheapest events will be run by the track.
If you go a little further you could also consider Pitt Race (formerly BeaveRun):
https://pittrace.com/
On the main page, if you hover on "Performance Driving", then hover on "Performance Events" within that, you can see the organizations that run events there (in addition to the track run events). There is also a calendar but it is a little clunky.
Pitt Race is almost as good as Mid Ohio and has better facilities.