Stablecoins like USDC are basically x coins is the cost. It’s pegged to the US dollar so 1 USDC is equal to $1 USD, always. Something like Bitcoin on the other hand, it’s better to think of it as it’s own currency. For example, right now the equivalent to $20 USD would be 0.00016962 BTC. When BTC goes up in price, $20 USD costs fewer Bitcoins (sats, which are everything passed the decimal).

The real world equivalent would be exchange rates, like between the US and Canada. Say the rate is 1.33, so that $20 USD game would cost $26.60 CAD. The rate changes to 1.35, so now it costs you $27. Next week it dips to 1.28, so now that $20 USD game costs $25.60 CAD.