What's a restored '66 worth, included bigger, newer engine (1500 cc?)
This site has pretty solid info for checking the value of used & collectible cars: http://www.nadaguides.com/. Their pricing depends on ZIP code, and you'll need to tell them whether your Beetle is a sedan or convertible. Unfortunately, adding non-original parts to an older car makes determining its value harder, because the car's no longer original. The best determination of its value will be the price you manage to get for it.
Average retail value is somewhere in the $5000 range, maybe a little more if its completely restored and in great shape.