Note: Buy a seed-maker before using this cheat.
You can get ALOT of money by doing the following:

1. Buy as many seeds as you want(Banana seeds are known to be best).
2. Plant them ALL, one diagnol from another.
3. Take good care of them until harvesting season.
4. When ready, harvest the trees.
5. Place every plant in the seed maker.
6. After the seeds are finished (three days for each 12 crops), you should have ALOT of seeds.
7. Sell all of these seeds to Van for ALOT of money, usually over 30,000 G![Hint: Keep some of the seeds to plant so you can make more money every year.]
8. Repeat the process with your extra seeds.