How to add quantity-based discounts to the bulk variations grid
Used alone, the WooCommerce Bulk Variations plugin is designed to allow you to manage and display variations in bulk. It doesn't affect what prices customers are charged for the variations they select from the grid.
By definition, the format of the bulk variations grid encourages customers to buy variations in bulk. As a result, it makes sense to add financial incentives to encourage them to buy in larger quantities. You can do this by using WooCommerce Bulk Variations alongside our other plugin, WooCommerce Discount Manager.
WooCommerce Discount Manager lets you add a wide range of pricing rules to your store, including quantity-based discounts.

You can optionally display a tiered pricing table on the product page so that customers can see how much they will save by buying in larger quantities:

When you use either the Simple Discount or Bulk Pricing discount types in WooCommerce Discount Manager on any of the variations displayed in the bulk variations grid, the total cost shown underneath the grid will automatically show the discounted prices. For example, if you select enough variations to qualify for a bulk pricing volume discount, then the reduced price will be shown.