What you're looking for is a lookup system. Rather than try to explain it all, it was easier to set up a quick example spreadsheet. Hopefully, you are able to get some ideas from this.

Here's a screen shot. The table at the top (in yellow) is the source information. The Crop column is also the source for the dropdowns in the lower section. Changing the crop will change the price and Fert cost based on the lookup table at the top. Changing any of the variables in the lookup table will immediately change any fields with the same crop.

The formula for Price for the NE corner field is this:

=VLOOKUP(B8,$A$2:$D$4,2,FALSE)

B8 refers to the cell in yellow with wheat in it.

Example Lookup.xlsx (9KB - 145 downloads)