I have a couple of the Prohunter 6-18X40 SF scopes and I regularly use them on a couple of centerfire rifles I shoot regularly at range. Largest caliber with scope is a 30-06 and lots of rounds fired with scope and no problems. Optics not great, but decent and have no problems with clarity/focus and etc. Check Natchez shooters supply site for Prohunters....probably lowest priced ones on internet will be found there.
Another brand of scope available from Natchez at discounted prices are the Nitrex scopes. Nitrex is owned by ATK, who also owns Weaver scope company. I ordered a Nitrex TR2 model 3-15X44 SF two days ago. The TR2s are Weavers super slams models. Nitrex has a rebate of either $50 or $100 on TR one or TR2 models. So, with rebate I bought my scope for $218....from SWFA price would have been around $320. If I'd ordered the Weaver brand super slam...price is $440. So, peruse the Nitrex models at Natchez.
Another scope to consider is the Swift Premier model 669M, a 6-18X44 AO scope. You can find it for $125 (plus about $13 shipping) at Amazon.com......careful, two other companies listed on Amazon are selling the 669M for about $216 and SWFA sells it for $264. I have two of the $125 669M Swift scopes and its a darn good scope. Swift is an American company making optics product since 1920s and they make their own glass and Premier models have a lifetime warranty. Google Swift scope and read reviews and comments about Swift scopes. You'll be hard pressed to find anything negative about their scopes.