Problems with "Hollowing Out" a model to save money

I am having the strangest issue.

I have created a model and I priced it "solid"- with no extra areas left empty.

I started hollowing out my model to reduce the total material it would need to use to be created- updating my model as I went to see how much the cost was reduced.

Then the price started going back up even as I reduced the interior of the model further.

I am using a boolean subtraction. Is there a better way to do this or a proper way the Shapeways would recommend?

At present, my model hollowed out to what I would estimate as 40% less volume is coming out more expensive than when I price the original "solid" model.

With the pricing, you're seeing the volume discount that's applied to WSF - more information on the White Strong & Flexible materials page

Also, make sure you have a hole joining the hollow space to the outside world.

Ahh, I had no idea there was a "volume" discount. So, basically, at this point, it would make my model cheaper to add a useless cube to bring it back down to the lowest price point that I was able to reach! :laughing:

yep... more about that here;
https://www.shapeways.com/forum/index.php?t=msg&goto=2746 5&#msg_27465

Wow. Well, I guess I'm about to start a collection of dice!