I have spoke with programming on this, for now, you are correct. With no Accounting - delete the imported jobs, make sure all the supply properties have the correct cost and import the data again, will be the quickest fix. I have requested a cost box be added into the Temp Tax mix ingredients area for a future Update.
With Accounting users, the Temp Tank Mix should be placing negative qty amounts into inventory as the ingredient inventory items. When recording the purchases at a later time, should be making an automatic journal entry to update costs the field crop enterprises. If this is not happening please let me know. We can look at this and see what can be changed there as well.