Controlling printing costs
Most printers charge by the cubic centimeter of material made. Some may add a "handling" charge. So you, as a designer, want to minimize the amount of material used. A few things you can do are as follows:
Shop around for a printer who charges less.
Use a less expensive material.
Make your object smaller.
Hollow out your object.
Remove unneeded material, in the lunar lander, the fuel tank clusters were built as a single hollow object instead of individual tanks. The landing pad is not a solid block; underneath, it's like an upside down soda crate. The rocket motors are not solid.
Delete unneeded details.