You mention the key feature for ddos (self-)protection - zero ingress fees. Non-Availability hurts you in harder-to-quantify terms than a bill for bandwidth used.

Zero ingress puts the upfront bandwidth cost onto the attacker. Because... you actually may succeed to defend and stay up. Their success is not guaranteed, they might be shouting into the void.

Attack success (as in, "impact on you") is guaranteed if your ingress is chargeable.