Though hard to swallow, that does sound like a reasonable price.
I changed my water pump on a Ford conventional bus with the 6.6 liter and the part listed for about $450 if i remember correctly. I did end up getting the part for cheaper, but that's a long story. I don't know what a fan clutch might cost, but i immagine they cost a couple hundred bucks at least.
On top of the expensive parts, your engine is probably difficult to get to immagine, since it's a flat front end bus. Labor is expensive.
just my $.02
what a drag that you broke down, especially with the legendary Dt466