An entire new Claris RD can be had for fourteen to twenty-five dollars. Again depending on model. If this is an old claris, you might not find it, or maybe not as inexpensive.

Don't assume a new Claris rear derailleur will work with the shifters you have. I don't know myself either way.


edit:
Oh... if I'd read all your post I wouldn't have stated something you already knew.