I buy blank (unthreaded) screws from TOTW or if I want something special I make them. I buy them in lots of 10 or more (#8 & #10) so I have enough on hand .
I make all my screws,mostly for locks but once in a while for other purposes.
In 1964 I bought a new Model 618 Atlas lathe and 10 years later changed it
to a machine dedicated to screws as needed and to establish the thickness of a
lock tumbler and leaving the small shaft to go thru the bridle oversize.
As far as the cost of special screws is concerned,the fact they are available at ANY price
should be considered but it won't be.
Bob Roller