Cool resource, thanks for sharing!
I gave it a spin and was initially surprised that the "affordability" index for my current HCOL zipcode is better than for my soon-to-be-home LCOL zipcode.
The difference is that average income in the LCOL area is much lower. (To reference another recent thread, my current zip is 93, or in the upper 7% of U.S. zips. The new once is in the 50's.) So, even though housing is much cheaper, as a percentage of typical income, it's more expensive.
So great resource, but mind the numerator and denominator.