Pricing for crops

below are some crops I think we could add in the game and their associated seed costs and sell prices.
the function I'm using right now to determine the sell price is sell(cost) = round(cost + 5.04 * cost ^ 0.352)

Crop | Buy Price | Sell Price
-- | -- | --
Carrots | 50 | 70
Corn | 60 | 81
Cauliflower | 80 | 104
Potato | 100 | 125
Pepper | 130 | 158
Watermellon | 150 | 179
Sunflower | 280 | 317

No files or tests are named. Start by locating the existing crop and pricing definitions in the Java game, then determine how the proposed crops and prices fit the current design; done means the agreed crops are available with their specified buy and sell prices.

Written by the indexing model from the issue text.