I'm no monkey wrench expert but I haven't heard of this maker. It's on Etsy for $30 shipped.

Still looking around on Etsy and here's 4 more for about $47 shipped.

Girard, of Girard Pennsylvania was a well known maker of monkey wrenches. A friend of mine has 18 different Girard monkey wrenches! He is not a collector, he just liked the first one he saw and didn't stop buying for a while.