Hi,
I'm not following you. I'm afraid we first need more details before we can answer you.
Are you saying that the total price is $30 below 300 and then above that, the total price is 0.18*number of items ?
I count 140 prices in your table, while you're talking about 64 variants.
What are the variants ? Is the quantity selected by the customer through a characteristic dropdown ? A select quantity input ?
What is the link between mass actions and configuring the prices for the different variants of the product ?