The prices for these things seem to vary quite a bit from $40 a pair
down to the least expensive I have found from Lee-Valley tool. $11.50
a pair or $10.50 if you buy three or more pairs. They carry four
strengths, 1.5, 2.0. 2.5 and 3.0.

http://www.leevalley.com/wood/page.a...=1,42207,42216

BTW: I have bought from Lee Valley for years and they are a first class
outfit. If you are into woodworking or gardening, they are the place
to go.

- John