Technical 4 inch Merc crank value question

A local guy has a 4" flathead Merc crank he offered to sell to me. At a glance, it appeared to be serviceable with just a polish, but I will assume that it needs to be ground for safety's sake. What's a fair price for one of these?

 

IMO, and not being from Kansas,$200-$350 depending on how “bad” the owner wants to sell it just to get rid of it or is “savvy” on what he has.

 

A standard size crank has a lot more value for the guys wanting to offset grind it.

 

I paid $400.00 for a standard size one in 2004, so if it's useable and still available that does not seem too bad of a deal.