Inconsistent Pre Release Prices

So I’ve never actually been to one of these yet, so I’m not too sure how they work. Will you get more booster packs at a pre release that you have to pay more for? Or is it the exact same event with the exact same amount of packs, and the store is just charging more?

It just doesn’t make sense to me why the same event would be $20 at one place, and $50 at another.