i modified the file a bit - all calculations are made in the script so the chart expression to be simple.
Regarding dimension presentation in this case ther is 2 dimensions PRICE and QRT and if you navigate to "Axes" tab and select "Continuous" in "Dimension axes" part the Static Max and Static Step became enabled. So Static Max = 900 and Static Step = 200. And in "Number" tab set "Continuous X-Axis" to "Money".
I know i can't explain good so the attached file may help you more :-)
Hope that helps!