The lock assembly (lock, cable, latch) cost about £40 when I bought it a couple of years ago. There was also the alternative of buying a complete ignition lock and seat lock/latch assembly replacement kit (intended for the TBS), but at over £200 I gave it a miss. Don't know the part number for that.
Part of the reason for the price difference, I think, was that the cheaper seat lock assemby had a plain zinc coloured finish (which I painted black) and lacked the chrome/red touches found on the ignition key barrel and original seat lock barrel as shown in this picture posted by Hyzer a few years ago:
This is mine:
Linear Mode
