The problem isn't how expensive the repair is. It's how cheap the alternatives are. Right now KEH has a couple of excellent 645s for sale at $300. That includes a 120 insert. I don't know how big Bighead's lens collection is but if it's just the 75mm then he might even consider one of the other camera types.

My 645 is acting up. I know sooner or later I'll likely get it fixed. But I decided to put the money towards a Bronica ETRSI kit instead for now. I gain some things then Pentax didn't have. I lose metering unless I find a cheap metering prism. Still over all it seemed the right choice for me.