Over the last few decades, there has been a renewed interest in the offshore wind sector. In particular, floating wind turbines represent the next frontier in the wind power industry. Currently, only research prototypes exist, and few studies are available on their possible investment cost. Therefore, a cost assessment for this technology is necessary to ascertain whether it is economically sustainable. This paper develops a life cycle cost model for floating offshore wind farms, bringing together the most up-to-date data and parametric equations from databases and literature. The cost model considers the key parameters of the wind power economy, namely CAPEX, OPEX, DECEX and LCOE. The proposed model should be helpful for future decision-making, as the wind energy industry is in constant evolution. An application to an offshore floating wind farms is also carried out, in which the three main types of floaters are considered, namely the Semi-Submersible Platform, the Spar Buoy and the Tension Leg Platform. An average LCOE of 9.74 c/kWh was found, at the lower bound of the typical range applying to fixed base offshore wind farms, and higher than typical values applying to onshore wind farms.