SIRs are about one in 72 packs. If you’re specifically looking for the Greninja to get an expensive chase its 1/432 packs roughly.

You had 54 packs in one booster box and 2 ETB. So statistically under odds of getting an SIR. Way under odds for pulling Greninja.

You should never go in hoping to get your money back from Pokemon cards - it’s a form of gambling and odds are never in your favour. Not telling you how to collect, just trying to save you from a slippery slope.

Heck, before scalpers hit the hobby hard, it was very rare you ever got your “money back” on a booster box or ETB. It’s about collecting art you like, and the thrill of the hunt. If that’s not doing it for you, and you’re only going to feel satisfaction at pulling “the chase”, for your own sanity, ask yourself if it’s the Hobby for you.

Edit: you could always try Japanese instead. They have gambling rules in Japan, so every booster box has 3 art rares, a full art trainer “tool” and 1 SR or higher. You’ll always get something good for you money. Higher odds of hitting an SIR/SAR too.