Rough answer I would say based on watching previous auctions is $1500 for a good condition Mark III. This might be a little high but with so few selling over a year it's sometimes hard to see where the average price is. Condition really seems to drive the price on these right now.
“There are invisible rulers who control the destinies of millions. It is not generally realized to what extent the words and actions of our most influential public men are dictated by shrewd persons operating behind the scenes.”