We had, after firing it with the stock scope, contemplated how you could turn the Walmart $298 Remington into a decent rifle and still stay under $500. We came up with Redfield Scopes, a scope company recently purchased by Leupold. Specifically there Revenge with the accu-ranger feature found locally for $177 (someone said they thought Dick's had them but I hadn't had a chance to check)

http://redfield.com/redfield-revenge/

Not sure how this goes with a sniper quality scope, however. Sorry.