Supercharger idler pulley

Up for sale is a (4) groove idler pulley. Apparently this is hard to find. I tried to find another so I could put a realistic price on this one and couldn't. I'm asking $400 or trade for 3 groove cragar style pulleys or cragar supercharger accessories.
Spec are
4 5/8 Od
1 7/8 I'd
2 inches wide