This study evaluates the levelised cost of hydrogen (LCOH) dynamically produced using the two dominant electrolysis technologies, directly connected to wind turbines or photovoltaic (PV) panels in regions of Australia designated as hydrogen hubs. Hourly data are utilised to size the components required to meet the hydrogen demand. The dynamic efficiency of each electrolysis technology, as a function of input power, along with its operating characteristics and overload capacity are employed to estimate flexible hydrogen production. A sensitivity analysis is then conducted to capture the behaviour of the LCOH in response to inherent uncertainty in critical financial and technical factors. Additionally, the study investigates the trade-offs between carbon cost and lifecycle emissions of green hydrogen. This approach is applied to ascertain the impact of internalising environmental costs on the cost-competitiveness of green hydrogen compared to grey hydrogen. The economic modelling is developed based on the Association for the Advancement of Cost Engineering (AACE) guidelines. The findings indicate that scale-up is key to reducing the LCOH by a meaningful amount. However, scale-up alone is insufficient to reach the target value of AUD 3 (USD 2), except for PV-based plant in the Pilbara region. Lowered financial costs from scale-up can make the target value achievable for PV-based plants in Gladstone and Townsville, and for wind-based plants in the Eyre Peninsula and Pilbara regions. For other hubs, a lower electricity cost is required, as it accounts for the largest portion of the LCOH.