There is already a local variable error. Thrown when updating a variable 2 diffrent times in a script

I have coded a script that keeps track of a money balance when buying various things.
I have defined the money variable at the beginning of the script with public var money : float = 1000; with 1000 being the starting balance. Updating the variable later in the script with var money = money - fieldCost works perfectly fine for subtracting fieldCost from money, but when using that and, later in the script var money = money - gardenCost to subtract gardenCost from money, compiler throws: NullReferenceException: Object reference not set to an instance of an object on the line of the var money = money - gardenCost. (yes, its a farm game) I might be just noobing this, as I am one, but it is the only thing preventing my game from running and I just can’t figure it out!

I haven’t yet written the code that sets the boughtField and boughtGarden to true, should that matter.

Code:

#pragma strict

public var money : float = 1000;
public internal var boughtField : boolean = false;
public var fieldCost : float = 150;
public internal var boughtGarden : boolean = false;
public var gardenCost : float = 100;

function Start () {

}

function Update () {
	//print balance to console
//	Debug.Log("CurrentBalance is " + money);
	//run buyplot function
	BuyPlot ();
}

// processes when player has bought something
function BuyPlot () {
	//has the player bought a field?
	if (boughtField == true) {
		//do they have enough money to buy a field
		if (money >= fieldCost) {
			//enough money, purchase field
			var money = money - fieldCost;
		}
		//not enough money, sends message
		else {
			Debug.Log("Not enough money to purchase Field!");
		}
	}
	
	//has the player bought a garden?
	if (boughtGarden == true) {
		//do they have enough money
		if (money >= gardenCost) {
			//enough money, purchase garden
			var money = money - gardenCost;
		}
		//not enough money, send message
		else {
			Debug.Log("Not enough Money to buy Garden!");
		}
	}
}

Remove “var” from the inner references

Example

var money = money - fieldCost;

to this

money = money - fieldCost;