Offshore wind and wave energy are co-located resources, and both the offshore wind and wave energy industries are driven to reduce costs while maintaining or increasing power production within developments. Due to the maturity of offshore wind technology and continued growth of both offshore floating wind and wave energy converter (WEC) technology, there is new opportunity within the offshore renewable energy sector to combine wind and wave technologies in the same leased ocean space through co-located array development. Combining wind and wave energy technologies through co-location is projected to have synergistic effects that reduce direct and indirect costs for developments. While several of these effects have been quantified, many have not been related to cost, and there is currently no cost model that incorporates all of these effects. Further, in areas where fixed-bottom offshore wind structures are infeasible, floating offshore wind platforms could provide access to plentiful resource further offshore. In this paper, we develop a cost model that represents co-located array developments, particularly for floating offshore wind and wave energy converter technology, and identify research gaps and uncertainties to be minimized in future work.