Spreading percent based upon criteria

Hi all, I've been trying to figure out how to do this for the past couple of hours.

Basically, I want to spread out a percent (lowest being 4% and highest being 10%) based upon cost-of-living (COL) criteria. I've reindexed it so I already have the column set up where the 4% would go to the lowest COL (0.5% in this case, since am not assigning the percent to any of the negative values shown in the '3rd Step' column) and 10% would go to the highest COL of 51.8%. All the values between .5% and 51.8% would fall in between being assigned 4% to 10% cost-of-living funds.

How would I go about setting this up? I have no clue where to begin. I'm attaching the file to show you what I'm talking about.

Thanks very much in advance for your help!