The Low Carbon Contracts Company (LCCC), which handles all of the CfDs on behalf of the UK government, said the developers had made a "substantial commitment" to the project.
LCCC said Dudgeon had reached the same milestone as Dong Energy's Burbo Bank Extension, which announced it had spent 10% of expected project costs last week.
The two projects were handed final investment decision enabling CfD subsidies in April 2014. The contract guarantees a fixed price for the electricity produced over 15 years.
Statoil and Statkraft have reached the landmark by agreeing a number of supplier contracts for the project, including a turbine order to Siemens for its 6MW turbine.
Sif Group, VBMS (formerly VSMC), JDR Cables, ABB, and A2Sea have all also won deals.
Dudgeon's onshore construction began in March, as the substation and cables started to be installed. It is due online next year.
