Creating a responsive plot chart?

Hi all,

My goal is to create a graph that has X-Y axis (Cost of Risk $ vs. Impact of Risk $). The user will input values into the two separate tables from drop downs under the respective headers (Cost and Impact).

I would like the graph to be able to do 2 things:

1) Plot the point on the in the graph space where the Risk would reside, given the dollar inputs (Cost and Impact) from the user.

2) Given the placement of the point of the Risk, the graph should be able to tell the user whether it is a good idea or not to consider investing in fixing the Risk (i.e. If the Impact of Risk $ > Cost of Risk $, than the user should invest to fix that risk). Could be done by leveraging a 45 degree line coming from the origin? Whereby anything to the right of the 45 degree line means the user should not fix the risky situation (since cost > impact) and if the risk lies anything to the left of the 45 degree line (impact > cost), the user should invest in fixing the risky situation.

I'd also like to have bowed out zones stemming from the origin, getting darker as the cost and impact increase (i.e. yellow, orange, red, dark red).

I have attached a picture of what the end-result graph would look like. I know how to create the back-end input data. But what I'd like to know is how to get Excel to tell the user to invest in mitigating the risk or not, given its relative placement on the graph.

Any help would be much appreciated.