Start a new game on Easy and then sell the plough and the shield. Harvest all the crops (or the ones you desire) and sell the harvested crops at the sell points where you will get the highest price for them. Sell the crops in the silos. If done correctly, you should have earned enough money to upgrade your combine harvester, tractor, and other tools or equipment.
Note: $210,000 is required for this trick. Speed up time and wait for a Deutz sale that offers 20% off your purchase. When such a sale starts, slow time to normal and purchase the Deutz 7250 for $210,000. Immediately turn around and sell it to the shop in the yellow square for around $220,000, giving you a profit of $10,000 on a single transaction. You can do this with more than one tractor at a time, which could mean around $90,000 in profit over the course of a couple of minutes if you sell 9 tractors (if you have sufficient starting funds).