I was thinking about getting one of these seats for $65 plus shipping, they look pretty nice for the money. Their not exactly like the original but their close enough for me. The only one's I've seen that look exactly like the originals cost $240 plus shipping.
eBay Motors: HONDA CT70 KO ST50 BRAND NEW SEAT UNIT (item 230159737228 end time Sep-06-07 10:20:33 PDT) Honda CT70 Honda 70 Honda Minitrail NOS Parts and services Kitaco and Takegawa performance parts classic honda minitrails. Look near the bottom of the page on the second link.