The problem here is that "save" doesn't actually mean "use less than before". It has a more complicated meaning, along the idea of conserving an important resource that would otherwise be lost. For example, if I want to say "people used less water after the drought started" I wouldn't say the drought resulted in water savings, not in the same way I'd say that of people taking showers instead of baths. In order to "save" a resource by using it less you need the lesser use to result in more of the resource being available for other or future uses.
So the opposite is indeed "waste", i.e. use the resource more in a way that results in less being available for other or future uses.
To use your example that objects to this :
"A sample: "I changed our subscription to something worse and cheaper to save money" vs "I changed our subscription to something better and more expensive to waste money"?"
The issue is that you wouldn't change your subscription to something better or more expensive to [anything] money ! While saving money is a goal for getting a cheaper and worse subscription, your goal in getting a more expensive subscription is clearly to get a better subscription, not to use more money ! So you would say "I spent more money on a more expensive subscription to get better service". The accent wouldn't be on using more or less money at all, because the original use of "save" wasn't really about the amount of money used either - it was about the concept of allocating your money away from the subscription and towards things you find more valuable.
And so there isn't really an antonym to "save" in this context because it isn't a binary situation; you could have an infinite number of goals and priorities that determine what you do about your subscription, and they'd each have a verb or expression of their own. And if that goal was to spend more money (you need to impress the Jones', your department needs to use up its funding before the end of the year or it will be cut), then you'd probably just say "spending more money".