Manufacture for Free
Go to Start a New Manufacturing Job from the list of items. When the window pops up asking you how many units you want and how many engineers leave both values at 0. Just click OK then quit from the list of items to the main menufacturing screen. You selection will be listed as normal with 0 units 0 engineers. Now go to change the values of the manufacturing job and change the number of units to just 1. This 1 unit will then be manufactured in the same time as normal but for free plus it won't use any materials.