I'll affirm Nick's 2x, but try to give a rationale: at the point where you have a reasonable business plan, you should not only have a cost and schedule estimate, but you should also have some sort of contingency estimate for cost and schedule that should be risked based, and is for dealing with at least the known unknowns. So, that 2x number is another way of saying the correct contingency going into a business like this is 100%. I think that is true for BOTH cost and schedule in this case. OK, why is that reasonable? Because there are so many known unknowns that CAN'T necessarily be resolved before you start to execute. That is because they are items that are out of your control: time for response from federal, state, county, and local entities; permit approval requirements; specifics of some of the equipment requirements once your process has been optimized, etc. Maybe, if you were starting a distillery that were a clone of one you had previously been operating, you could reduce that down to 50%. Or 30%. But mostly we are talking about first time start ups, and in that case, the 100% contingency seems completely reasonable, IF YOU HAVE A GOOD ESTIMATE to begin with!
JMHO