I had already looked into that. On the original web-site (which may actually be the one you are quoting), he gives detailed instructions on how to modify those gears to work on the CD. The effort is a bit extensive, so that may be where a lot of the cost comes from.
Basically, you buy the original gears, sand the plastic down a bit to make their surfaces rough enough so they can be glued together, glue them in a specific position, then drill out the center holes with a specific size drill bit (done either by hand or with a very small, slow drill). Keeping the two gears co-centric requires either really good hand-eye co-ordination, or a very well machined jig.
I suppose part of the cost is also shipping, and currency conversion.
Just some FYI
Charlie