Flex - Sending a parameter to a custom ItemRenderer?

What I am trying to accomplish to to get financial data in my Flex Datagrid to be color-coded--green if it's positive; red if it's negative. This would be fairly straightforward if the column I want colored was part of the dataProvider. Instead, I am calculating it based on two other columns that are part of the dataProvider. That would still be fairly straightforward because I could just calculate it again in the ItemRenderer, but another part of the calculation is based on the value of a textBox. So, what I think I need to be able to do is send the value of the textBox to the custom ItemRenderer, but since that value is stored in the main MXML Application, I don't know how to access it. Sending it as a parameter seems like the best way, but perhaps there's another.

Here is the current code for my ItemRenderer:

package {
import mx.controls.Label;
import mx.controls.listClasses.*;

public class PriceLabel extends Label {
    private const POSITIVE_COLOR:uint = 0x458B00 // Green
    private const NEGATIVE_COLOR:uint = 0xFF0000; // Red 

    override protected function updateDisplayList(unscaledWidth:Number, unscaledHeight:Number):void {
        super.updateDisplayList(unscaledWidth, unscaledHeight);

        /* Set the font color based on the item price. */
        setStyle("color", (data.AvailableFunding >= 0) ? NEGATIVE_COLOR : POSITIVE_COLOR);
    }
}

(data.AvailableFunding doesn't exist)

So does anyone know how I would go about accomplishing this?

You may want to look into ClassFactory from the Flex APIs:

This allows you to set a prototype Object with arbitrary types / values each of which will be passed to the item renderer. From the sample:

var productRenderer:ClassFactory = new ClassFactory(ProductRenderer);
productRenderer.properties = { showProductImage: true };
myList.itemRenderer = productRenderer;

The above code assumed that "ProductRenderer" has a public property called "showProductImage" which will be set with a value of "true."