At the next mold change, one person with a stopwatch times four parts: the wait for what is fetched, the swap of the molds, connecting the water, and the start-up to the first good part.
Cost
Under $100 of one person's time, to watch one mold change and write it up. Nothing is bought, and the change is one the plant makes anyway.
Duration
One mold change, then a quarter of an hour of notes
Confirmed if
The press waits more than about 8 minutes for the mold, hoses or tools. Then the carts pay for themselves within a year.
Ruled out if
The mold, hoses and tools are already at the press when it stops. Then a cart has nothing to save.