It is all very interesting
After some more research I have found my lowest cost option would be a direct from china conversion kit through ebay. from the photos it is the same hardware that is being offered from UK bases suppliers. the risk being if there is a problem with it there will not be any after sale support.
I am an electrical engineer so I am pretty confident I can sort out any electrical problems. Any mechanical problems though would be harder for me to fix.
I have seen a few build blogs for similar bikes to mine with both front and rear mounted motors and both seem to have been successful
I am still inclined to buy a front motor as I think it will be much simpler for me to fit and keeping cost down is important to me