There are 2 options forming var1 (the first value of the stockpile).
First of you have the faction, this is pretty easy. The values 0-9 represent the different castles - 0 and 1 being commoners and outlaws and 2-9 castles. While 0 and 1 won't have any effect on the game, setting it to 2-9 will generate 20% of the buying price in the money chest of that castle for every purchase. You'll probably want to link most stockpiles to a castle.
Then you have the price multiplier. When you press F2 and scroll down, you'll find a list of numbers and percentages. These represent the price multipliers. While 0x (x represents the faction value) is the default price, it ranges from 20% of this default price (1x) to up to 1000% (12x). Beware though: Mostly you'll need to reload the scene (restarting) if you want to see the actual price in the editor.
To form var1 you'll simply combine these two numbers - for example 75 will set the price of the stockpile to 160% of the default price and 20% of that price will go to the money chest of castle 4.