Can drupal commerce products become cheaper to the customer when they order more?
Assuming you're on Drupal 7 yes, I've done this with the Commerce Price Table module: https://www.drupal.org/project/commerce_price_table

"This is a contributed module for Drupal Commerce that allows you to use a secondary price field to supply an alternate price for a product based on the quantity of that product on the line item. It also provides a field formatter to display the price/quantity values as a table."