I haven't looked at prices since I sold my low grade Mantles in 2010 and 2012.
I sold them for a fraction of what they go for now. Based on the trends I'm seeing it's a stronger market now and people have the coin.
I never did upgrade and it's probably a losing proposition now.
These are just an example of low grade options but they seem to have doubled in price.
Just for reference I got just under $7k for the '52 and under $5k for the '51.
