Payment Button: If I want different prices for different services, do I need to purchase an upgrade?

You don't need to upgrade to a paid plan if you want to add different prices for different services in your Payment Button app. You will need to simply create separate buttons for every service you have. This is free of charge also as the way POWr pricing model works is that you pay for the functionality of a specific app, not for the number of apps you can create. So, when you buy a Starter plan for a Payment Button app, for example, you get access to Starter features of this app and get to create as many Payment buttons with Starter features available as you want.