Unlock lets you pick the price, but also the currency used by your membership. This means that you can, for example, use a stable coin such as DAI or USDC to have a price-stable in $. Alternatively, you can change the price of your lock at any point if you need to maintain relative stability, but make sure you do not choose a highly volatile currency. Finally, you could also leverage your lock’s “hook” capabilities to alter the price of the key, but that is generally considered a lot harder to implement (and would require the help of a developer).