Please don't make duplicate topics, as you already have one asking about buying a Proton Pack: link
Just so you're aware, Proton Packs aren't advertised for sale every day, there can often be long stretches of time between listings, which are usually made in the marketplace. It should also be noted that $500 would only get you a very basic (no light or sound) Proton Pack, as often the better-quality shells can cost close to that.
Feeling overwhelmed by the Covid-19 pandemic? Please visit The Support Thread.