I think that when they say that all magic comes with a price, they refer to the people who use magic, even when they got it from someone else, to gain something for themselves. Like the people who made deals with Rumple had to pay that price.
Rumple is actually careful not to use magic for anything too serious. For example, he isn’t the one who enacted the curse, so the possible repercussions of that move didn’t affect him.
I’m not sure we can say that Rumple brought magic to SB. He rather brought it back to the land that had lost it due to the dark curse. Magic had been the natural element of this world before the curse. I’m not sure that’s the same thing and that there are going to be consequences. It can be treated as restoring the natural order of things. But I guess we will see.
The price for rejecting Bae and Belle, I think Rumple has already paid. He lost both of them to magic that he chose. He had to live without his son for centuries, and we still don’t know what had happened to him. He had to live for about 30 years believing that he indirectly caused Belle’s death. I’m not sure if paying the price has to involve losing someone permanently.