Hi Mel,
I picked one up not that brand but that size for $20 at a local Sunday markets in similar condition, what ever you do,do not try to restore it, the value will drop like you would not believe. Also it should have a very small date stamp somewhere that will give you the month/year of manufacture.
Forgot - the Spong No3 is the ideal grinder for espresso because of the burr wheel that gives the grind size, a number 3 should in about 30 turns give you enough for two espresso coffees.
Have been told by a coffee nut friend of ours your machine should sell for between $170 and $200(NEW) or today about 1/4 that price. The original company is English early 1800's to about 1963, the later model grinders had a plastic handle and are of less value $100 to $150. The company also made meat grinders, bean slicers and was sold to Salter the scale company in 1963.
Bob.