Crystal sets were old technology when I was a lad. 
I used to sell crystal sets to people when I was at school. That is where I came up with the ferrite rod tuning method, it was a cost down on the variable capacitor. I made the boxes out of cardboard and used to sell then for three and six ( 3/6 ) and it cost me about two shillings to make. Not sure what that is in new money.