quite a few crayford owners on BSC mate
they do come up every now and then, anything from 2G to 10 really.
Mk1 is very very very rare and the Mk5 was made by carbodies not crayford and a bit cheaper, a Mk4 or 5 project can be got for under a grand but expect welding !

http://www.buysellcortina.co.uk/forums/