Alright kids, breathe...a DDoS attack isn't the end of the world, it's just the internet throwing a tantrum. If you really don't want to use a fancy protection provider, you can still act like a grown-up: get your datacenter to filter trash at the edge, announce a more specific prefix with BGP so you can shift traffic, drop junk with strict ACLs, and turn on basic rate limiting so bots get bored. You can also tune your kernel so it doesn't faint at SYN storms, and if the firehose gets too big, pop out a more specific BGP prefix from a backup path or secondary router so you can pull production away from the burning IP.
Very quickly you'll find this doesn't work. Your DC will just null your IP. You'll switch to a new one and the attackers will too, the DC will null that one. You won't win at this game unless you're a very sizeable organization or are just willing to wait the attackers out, they will get bored eventually.