If that block is roughly 4.5cm x 4.5cm x 25cm then the volume of it is about 500cm³ which translates to 4.5kg of copper. At 11€/kg that makes about 50 euros.

Would you even notice, after buying the ram and storage?

Yes but you save on manufacturing.

Copper isn't that bad. It's not cheap exactly, but it's probably going to cost what an expensive CPU cooler already would.

11 euro per kilogram

What's a solid block of copper cost? one banana?