The starting plort values change over time, and will increase as days go on. The value of certain plorts will stall to a complete stop over the next several days, such as Pink Plorts. If a player cashes in +100 plorts the day before, the price will stagnant and get stuck at its former value.
This causes the market to behave as if the quantity of certain Plorts flooded the market, causing the price to hit an average based on demand. This encourages players to keep a variety of slimes on the ranch. A bar chart below shows the default values. A good starting strategy would be to make a silo and store all harvested plorts inside. Once the silo is full and the prices are favorable, turn in the plorts, which will maximize profit. But it should be kept in mind that to maximize your silo you will need to pay a total of 2,000 newbucks to purchase.