Take a Deutz-Fahr combine harvester, attach a header to it and go harvesting. By the time the truck arrives at the harvesting site, you have a bunker capacity of 13,500 liters of grain in reserve.
I made a mod of the Deutz-Fahr HTS 6095 combine harvester for harvesting in the farmers' game Farming Simulator 20. At the same time, I set the price for the machine at 249,000, and for the header at 34,000 money.