Supernatural Cliche?

I'm not sure if this would be a commonly used cliche but...

My MC turns into a Supernatural (what the race with power in my world is called) at the end of the novel. Cliche - or not?

Depends. Is it paranormal romance, or just supernatural? If it's paranormal romance, I've seen it done a couple times, which means it's probably been done many more. If it's just supernatural, I'm less familiar with that genre, but I haven't seen it. I would ask WHY you're turning your MC into a Supernatural at the end of the novel, though. Is this sequel-baiting? Fandom-baiting? Or has your MC been working toward this for the entire book and this is the fulfillment of their goals? If none of the above, what is the purpose?

I Like that you can only gain power by giving something up of equal value. When you say Supernatural is a race does it mean all supernatural being are lumped into that or are there other creatures that are of a different race but poses ablilites?

So far, what comes to mind is Goethe's Faust, although the whole human to supernatural transformation in Faust occurs right off the bat. In your story, it becomes the lesson, the conclusion. I can't remember any other story that does that, what you plan to do, but I think it's a common thing. It's not necessarily bad, in my opinion. I'd call it a staple of the genre. Bottom line, it probably is but it sounds like it'd work for your story. :)

All depends how it happens and why. If it's a prophecy or a family connection or being turned into a vampire thens it is a cliche.

"The Shadow Over Innsmouth" by H. P. Lovecraft.