The cheapest and most accurate boresighter in the world is a sharpy.haha.

Take a sharpy and make a 1/4 dot on a piece of paper, then make another 1/4 1 1/2 inch above the previous one.(depending on mounts base height 1 1/2 usually standard between barrel and center of scope). Then place your rifle 10 to 12ft away and clamp it down in a vise with the lower dot centered looking down the bore. (won't work in semi-auto's and you have to remove the bolt on bolt guns). Once you have the lower dot centered in the bore and the gun is locked solid adjust the scope to center the upper dot. And you just bore sighted your rifle cheap and more accurate than a gunsmith can do with expensive tools.

(Turn the scope down to lower magnafication)