For long range rifle shooting you need a high quality, reliable scope which, unfortunately will be pricey, often shooters spend more on a good scope than they do for the rifle it's mounted on, but a rifle is only as good as it's scope when you are shooting long range.
I use Leupold, but there are a few other makes which are also of high quality.
The biggest problem with the cheaper scopes is not optical quality, it is with the consistency and repeatability of the windage and elevation adjustments.
If you adjust 3 minutes of windage to the right and then adjust 3 minutes to the left to get back to 0 wind, cheaper scopes may not consistently come back to exactly 0 - maybe more, maybe less, and you will not know until your next shot is not where you wanted it to be. Similarly, if you adjust elevation up 26 clicks and then down 26 clicks you may not end at the same elevation as you started with when using a poor quality scope.
Sorry for the long-winded explanation, but I know from other shooters' experience that buying a cheap scope for long range shooting will result in complete frustration and in the long run, a waste of time and money.
Bottom line: buy a high quality scope.