That's easy, go to the CMP Sales webpage ... Rifle Sales - M1 Garand
If your rifle is as stated here... then their prices start at $1595.00
I guess it depends on a lot of other factors, and do you have the CMP certificate that came with the rifle when it was purchased from there? it makes a difference to most folks, but you can research the individual parts "drawing numbers and such too" and your serial number etc, at places like this one: M1 Garand Born on Date
Just depends on so many things, but these are places to start looking...