Need X-axis to show a set of numbers

Attached is a graph I'm working on. I'm happy with the margin curve trend line on the secondary axis (I hid the main line and data. I like the smoothed line more). The price curve is doing what I want.

What I can't seem to get right, is the cost to be listed at the bottom of the graph in the chart axis. I've tried inserting line chart and an X-Y chart (using 1 as the y-intercept). No luck

Any thoughts on how to get an x-Axis to display the cost column to the left in the data set? It should read $0.10 to $1,000.00.

Thanks much,

Roger!