I totally agree about getting on the track. A lot of people think they aren't into racing so they don't need to go to the track. Track days are NOT about racing. They are about improving skills in a safe (relatively) and controlled environment. I've seen all manner of bikes on the track from cruisers, touring rigs, adventurer bikes, super motards, standard naked bikes, and full blow sport bikes, etc,... Even ONE track day can do wonders for your riding skills and confidence. It really is a great experience. I watched a totally new rider on a brand new Ninja 250 go from wobbling through corners about to fall over to being totally smooth and relaxed by the end of one day. That is not unusual.
I never had to buy leathers. I had a textile suit and there was a zipper about 12" long at the base of the jacket that zipped to the pants. That was really the only big requirement. Other than buying some tap for blinkers, head light, and tail light, there really wasn't any serious expense. A lot of track days need corner workers. When I did mine, I was able to do the morning sessions and then corner work the afternoon sessions. The next time I corner worked the morning sessions, then did the afternoon sessions. I did not have to pay as a result of doing the corner work. I'm not sure if they still do that or maybe just give a discount for corner working. Even the corner working was cool though because you could really watch how different riders take the corners and you could see people improve over the course of the day.
My insurance covered my bike. I called them and explained that it was NOT racing and NOT a competitive event. It was "Closed course instruction". They had no problem with it. I can't recall if that was USAA at the time or Progressive. Either way, if you buy a used 400-450 and set it up, even if you wreck it, you aren't likely to be out much money for the bike.