Free: Contests & Raffles.
http://www.weaveroptics.com/rings_bases/rings/detachable_alum/extensiontopmount.aspx
You could put one of those 1 piece bases that is a rail type mount and then put the rings anywhere you want on it, but they always seemed to be kinda cumbersome for a hunting rifle to me. Makes the access to the chamber that much tighter. I never liked them, I'm sure there's other opinions on them better than mine though.