Crud! Them things are over 300 bucks!!
Get two peices of 1/4" aluminum sheet cut to about 3 or 4 feet long by two feet deep. Have a lip bent on each piece that is the thickness of the transom. Put them on the transom so that one lip lays over the other. Adjust to the right height and then bolt them to the transom (sandwich the transom between them with thru bolts). Probably 50 bucks or so, if I remember right.
After reading the post above mine, the idea is similar, but use two separate pieces instead of having a U in one piece.