I've had pretty good luck with cheaper scopes like the Simmons Prodiamond and Truglo shotguns scopes. I know a lot of guys pay more, but especially with the Simmons, I've put them through the ringer, dropped them, hunted in heavy rain, snow, etc. and no problems so far. As far as percentage, lets see....

#1. $120 rifle with $40 scope (Simmons) = 30%

#2. $160 rifle with $40 scope (Simmons) = $25%

#3. $170 rifle with $70 scope (Truglo) = 41%

On the other hand, if I would buy a $400 muzzy, I probably would not put a $40 scope on it- I would invest some more.