Noticed in originally on build 97, and verified still present in build 146, that any tinker's tool parts that you make only costs 1 ingot regardless of the part built. I've tested, and built a tough tool rod (expected cost of 3), blank plate (expected cost of 8), battle axe head (expected cost of 8); and all of them only used 1 ingot each time. Also a side note, when you try pouring with no mold, it makes a cross guard (also using only 1 ingot, expected to not pour).
I was not able to test if still present in build 156 (due to titanium parts not present).

Minecraft 1.7.10
forge mutlipart 1.1.0.300
mantle 0.31
tconstruct 1.6.0d40.1
mariculture 1.2.3d-146

I haven't changed this for a very long time (If at all). Making me believe, this has always been the case just noone has informed me until now :p. Looking at the code for the 1.6 version and it's all one ingot there too. /facepalm