Absolute cycle $195 walk-in, which is pretty good; However you will have to ask around to see what their rider density is like.
Clubs can run trackdays and charge people for much less simply by bumping up the rider density, but if the track is like a traffic jam it just became pointless, especially when clubs have passing rules. In addition some clubs are more gear towards newer riders or towards lowing risk at the track. Some will be just free for all. So when picking a club you should find one that fits how you want to ride.
Leathers you can rent, if you don’t want to invest. Unless you KNOW you are going to enjoy this, then get leather no problem; but if you are on the fence you might just wanna rent one and give track riding a go and see if that is what you enjoy.
Spectating during trackdays are usually free, but different tracks might have different policies.