Re: AR-15 mount
Pretty sure you mean cantilever, not offset. Yes,you will need this type of mount to obtain a proper cheekweld and eye relief with most magnified optics on the AR15.
For $100, the Burris PERP QD is a great option. For a bit more you can get into an American Defense MFG. mount. A little further would be LaRue and after that Bobro.
If you are not looking for a QD mount, there are many to be had in the $50 range. Burris, Weaver, RRA, Armalite and Primary Arms jusy to name a few.