$200-$300. There are a few decent $150 scopes, but the extra $50 of a $200 scope is huge. If anyone can squeeze $300 into their budget you start getting into a seriously good scope. Going above $300 gets you a better scope, but the value for the dollar goes way down. A $400 scope is only slightly better than a $300 scope. A $300 scope is MUCH better than a $250 scope.
Balking at spending $300 on a $400 rifle is not wise. There are lots of $400 rifles that perform just as well as $1,000 rifles. There are no $150 scopes anywhere near the quality of a $300 scope.