Generic materials choice diagram: massic price (kg/€, $ or whatever) vs. specific characteristic (IU/kg), linear scale.
The higher the abscissa, the lighter the part. Iso-price lines: the higher the slope of the line connecting the point representing the material with the origin, the more expensive the part.
<a href="//commons.wikimedia.org/wiki/User:Cdang" title="User:Cdang">Cdang</a>
<span class="int-own-work" lang="en">Own work</span>