I worked on a mid-sized online game a few years ago and we experienced several DDoS attacks. I recall one employee tracking down the specific botnet that was rented for the attack against us and we calculated the attacker probably spent a couple of hundred dollars based on the rates.

IIRC, we eventually used AWS Elastic Load Balancer to just soak up the attack, which was a pretty basic SYN flood. Then we waited the attacker out until he got sick of spending money. That temporary redirect definitely impacted performance and cost us some money but it pretty well mitigated the issue. We also spent a bit of time optimizing our servers to drop obvious nonsense requests as quickly as possible but in the end the ELB handled most of the issue for us.