Let crafters craft the precursor.
That would take a lot of RNG out of the equation and would stop blind dumb luck from making some people rich while others suffer grinding away.
Easy way to do this: sell the plans at a high cost, like 100 gold, and have only a 1 time use (which won’;t allow people to manufacture precursors nonstop). Make the precursor use 4 times the materials that normal exotics use with some extra materials thrown in like glyphs and other valuable stuff.
In the end a precursor should cost about 400g to make, but it takes a lot of the RNG out of it.