I'm very partial to the new Weaver's especially the Grandslam line. They utilize the "microtrak" adjustment system that has been on the Target series for quite awhile. the Weaver T series has been used by the Benchresters for quite a few years.

I've putthree of the Grandslams on Varmint rifles. Two 6-20's and one 4-14. These would excede your price range by about a $100. To stay in your range you would have to go with the 3.4-10x40. Bruno's have them for about 250
http://www.brunoshooters.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=BSS&Pro duct_Code=WEO800588&Category_Code=35WVGS