I'm Miles from the Social Care team at Shopify! Letting your customers choose prices is a great way to give back to people, and it's becoming increasingly popular!
There may be a way to code the changes you're after, so I'll leave that to our Partners and Experts to help with if there is a solution. In the meantime, there are some really cool apps you can download that will help you let your customers choose the price they pay. I've listed 2 app possibilities below for you, but if they aren't suitable, feel free to check out the Shopify App Store for more inspiration!
I hope these apps help you achieve your goals. Let us know if we can do anything else to help out.