Sorry, but if yer looking in jolly old London town then I can't offer much help. It sounds like a call for Dr. Shoe.
However, I would suggest that one approach might be a
cost plus basis by which you offer/contract for the boots on a estimated fixed price plus a fair markup for profit. Another approach, which I actually prefer, is to work from a reasonable estimate of labor and materials. If the bootmaker is worth his salt, then he should be able to give you an accurate estimate of the materials and a reasonable estimate on his labor (assuming that you don't expect a lot of unusual artistic work on the boots).
Now I have absolutely no idea what labor and materials are going for in London. But here in the states $50 - $70 per hour (depending on level of expertise) would be a reasonable rate for labor. I am very hesitant to offer any sort of suggestion on materials because I've never even watched boots being made and I have no idea what is involved. But, obviously, the cost of materials will depend upon both the quantity and the quality used.
There are, of course, many other ways to approach the matter, so I was merely offering a few suggestions. Good luck to you.
