Yep, should be absolutely fine with modded materials. The mod files do not reference materials in any way.

so this should have no issues with modded materials?

All materials are affected. A cow leather helm costs 15pts at embark, 30pts for copper, 150pts for iron, all 50% higher than normal. An objects value comes from the item value * the material value, plus quality and decoration. This mod changes the item values.

Is this just for copper?

NB values in preview image are 2x the description due to copper having a 2x material value.