Gosh I'd love to have this behemoth in my shop! Just look at it holding that 4" leg vise in its jaws, like a really awesome shark, about ready to tear apart a much less awesome shark! :P Too bad I don't have a spare $750 to throw around >_>

http://www.ebay.com/itm/EIGHT-INCH-8-in-JAWS-BLACKSMITH-POST-LEG-VISE-ANVIL-FORGE-GOOD-CONDITION-/221587019576?pt=LH_DefaultDomain_0&hash=item33979d9738

At $750 I'm not surprised it didn't sell - in the UK they fetch scrap metal prices at farm sales - on eBay.co.uk they sell for about £50, say $75 - much the same in France and the rest of Europe...

see: http://www.ebay.fr/itm/n-3-OUTIL-ANCIEN-gros-etau-de-serrage-26-kg-de-forgeron-forge-/370786536402?pt=FR_JG_Art_Objets_XXeme&hash=item5654998bd2 for 70 euros...

One year ago I purchased two at an auction for $8 for the pair.  Got a nice 4 inch for $10 another time.   Have a six inch jaw I woulldn't let go for less than $150.   So the prices are all over, problem with ebay is the shipping. 

4" are very common. I paid $27 for one at a flea market. But my 5.5" I payed $100 for, and that was a pretty good price for as nice a vise as it is. I've never seen a vise that big... The big ones are exceedingly rare, most of them got melted down for scrap. $750 probably isn't all that unreasonable, really. It's not a GOOD price, but I wouldn't be surprised if he could get it, as long as someone was local who wanted it...