Gobblin says we're over 25k. In any case, over 20k on the first day with tickets available to non-season-ticket holders is pretty darn good. Got about 6 weeks for more ticket sales. I have a hard time believing that another 20k or so won't sell over the next 6 weeks, especially as publicity increases closer to 11/14/15. Plus, you have to figure there will be quite a few walk-ups on the day of the event. With tickets costing about the same as a hot dog and a Coke, tailgaters will probably flock to the thing just to check out the spectacle and be able to say they were there.
I think 40k+ is a pretty safe bet at this point.