Giving the caliber might help in the evaluation; however, unless it is in some rare caliber, it does not have any significant collector value.
It is a nice rifle though, as are all M77's of this vintage.
The ST or Round Top is probably more rare than any long action RS (rings and sights) especially in any calibers except 30-06, 7 Mag. I have seen them in Flat Bolts, Hollow Bolts and of course Round bolts. Just today I saw a 338 ST - wish I had some extra cash to throw at it!