How much for a mint 1961 GF?
Sort of depends where you are. They're definitely cheaper in the UK than the US, especially if you're a US guy with dollars buying in pounds.
And when you say "Mint", what does that mean? A "Mint" coin means as from the mint, never circulated, absolutely perfect in every way. I don't think there are any GFs in this condition.
If you mean a bike that looks essentially new and unused in every way, and the running gear has been rebuilt to factory specs and has no wear on any of it ... I wouldn't know how to price something like that.
If you mean a really nice bike that runs perfectly, and would likely win or place high in a show if entered, then I'd say the US price would be around $10,000 for that. For a really nice bike that runs and is ridden, and looks like a new bike with 1000 miles on it, I'd say $8000 for that.
I have a nice GF with a completely rebuilt engine that runs perfectly, has a repro but stock-looking fender, a new Chronometric, nice paint and chrome, a new seat, Craven luggage, and is the envy of all who see her, and I gave £3600 total for it (£2400 purchase price, £1200 in upgrades and rebuilds). Back last year when I got it, that was $7300 - today it's $5100. That's my life story - always a day late to the party.
So that's me lot - others may have other experiences.
Lannis