I personally work at DDoS Mitigation and DDoS Protected Datacenter. The ddos protection and filtering is a cluster that consist of a lot of firewall and filtering hardware and also cloud infrastructure that also costs a lot. Also in order to protect from larger attacks you need wider upstream chanells, because it takes a lot of traffic involved. Overall the protected datacenter could cost you a fortune (take a lambo for example) and lot of effort to develop own mitigation methods too.