Any ideas on what a pre 64 Win model 70 feather weight in 243 cal is worth? The rifle is in very good plus condition.

Whatever the market will bear, unfortunately. I've seen them go between $650-$1150. As an example, I bid on and lost a 308 a few months back, selling price $1150. It has become harder to find featherweights that haven't been altered.

I have been doing the same as Donato - bought them at $650 to $750 and seen others sell higher. It is a function of age, condition and alterations.