Money is pretty easy to come by, no need to hex edit game saves. Stock pile your starter seeds in the box, put Citrus Maranta in a pot, self pollinate it until you get batches of 15 going. If you don't yet know what that seed looks like, plant all of your starter seeds, self pollinating the plants so you can get your starter seeds back. Box one of each and sell extras. Dragging seeds to the trash sells them. Make sure you keep ONE of each kind (I keep mine on the bottom row of the seed box so they are not confused with the others).
Keep growing that one until you can get the level 2 soil, took me like 3-4 rounds of just that plant, selling off excess seeds (beyond 15 pots worth).
Buy level 2 soil, start your cross breeding. You've spent 850, and by the time your first cross seeds are grown, you'll be back up to 500+ in the bank.
Once you've exhausted just a couple of tier 1 seed combinations, you will have more than enough for the level 3 soil, and more.
Don't get in a hurry to buy level 3 soil, if you have any organization in your breeding program, you won't experience any problems with plant health. Just avoid crossing your tier 2 seeds until you are complete with tier 1.
You cross tier 1 with tier 1 once you have the level 2 soil, until you have exhausted the combinations before moving to tier 2 cross breeding. If you want even more cash, you can keep a row of your first crosses going, self pollinating them to keep your seeds of course.
**If you want a good money maker, Jalapa Fern (Citrus Maranta & Spotted Astera) sells for $28. With seed sales, it's $600 per batch of 15. There's probably higher combinations that will bode well in level 2 soil also.
You DO NOT need to upgrade the Nursery to have good sales, just sell in batches of 10-15 plants and the crowds aren't an issue. Leave prices at default.