Dave you have to remember a few things, yes you can buy willow at any grade from the merchant we all know that.
You get returns, you get willow that won't perform and you get willow the is good/great. So you make the bat and this takes time, it could be good, it could be bad, it could be great but it is still your time, grading, shaping, pressing the damned thing.
So all of a sudden your return % on buying lower grade willow is lower then buying high grade willow is well not worth it based on that return.
It is really easy to say I'm going to buy £6 clefts and make my money on the upgrade but in all truthfulness it will never happen
As they say you don't get something for nothing