http://www.justauto.com.au/justbikes/motorcycles-for-sale/1969-HONDA-750CC-750-CB-JBFD4096441?backurl=http%3A%2F%2Fwww.justauto.com.au%2Fjustbikes

Sandcasts are rare but not that rare. It'd be a reasonable buy at about half the price. They made 7414 of them and generally the lower the number the more valuable. The number stamped on the frame of that one indicates it's one of the later ones. There were 3 or 4 prototypes that are worth huge money.

One for sale right now on ebay U.S.
https://www.ebay.com/itm/1969-Honda-CB/192510227754?hash=item2cd280f52a:g:A1QAAOSwEm1a0RzF&vxp=mtr

Nice bike. Had a K2 for about 18 months when I was 18-19. Tried every day to blow it up. I didn't succeed, it just kept going.

Agree its just the fact that its a relatively rare bike guess makes up some of the price