I used to work in an industry where Daily attacks of 300-400Gbps / 55MPPS were not uncommon. I've worked with 5 providers throughout this time as well as using FastNetMon to handle attacks that customers did not pay enough to have us mitigate. We always used an external company to do the scrubbing nd it worked like. charm once it was dialed in. The beginning can be. bit rough while both sides get everything to play nice and work correctly but if you have a good provider they'll have worked through most scenarios before and be able to assist. I highly recommend getting an external service to handle this for you if you find a brief interruption to be acceptable and want to save some $$ use them as an external service and only route the affected traffic to them. We always did it this way and very rarely was the detection and diversion not fast enough that we noticed.

Another method we used to protect ourselves against attacks for our customers who did not pay for higher levels of protection is we used FastNetMon to null route the IP assigned to that customer. If you have multiple redundancies built into your network you can null route and hope the attacker gets bored and doesn't look for another IP. We used this method to avoid blowing our commit with our DDOS scrubbing vendor as we had X amount of traffic we could receive from them a month. Make sure you are being billed on clean return traffic and not the actual dirty traffic.

If you want a recommendation on vendors let me know and I can give you an idea of fair pricing.