30% doesn't sound crazy, based on this first-order-approximative data: https://www.eia.gov/dnav/pet/hist/LeafHandler.ashx?n=PET&s=E...
Further, gas stations generally need to pay quite a bit to get gas shipped to them as it's heavy (12 gallons is over 75 pounds), dangerous, and often very far away.
So, cost at the refinery is very misleading.