Delivery fees vary from $4-10, plus tip.
And while tipping is technically optional, it's de facto required. The driver will see the total pay for a delivery before they accept it, and if it's too low, they'll reject it, and DoorDash will offer the delivery to another driver. If you don't tip, then your delivery will be rejected until it reaches some driver that's gotten desperate. By that time, your food will likely have been already made and sitting and waiting for 30 minutes.