I don't think anyone but ProVape REALLY knows - there's no "tube swap" price published...
But I have heard of ONE guy that got a tube swap done, while sending in for some other repair as well, I think.
So - it can't hurt to ask them...
If they say "no," I'd bet you could pull off a trade in the classifieds, or sell one and
buy a new white one with minimal overall net loss - a good condition used ProVari really holds its value!