Use Barrow to upgrade the Shipyards on my board to Coal era, using one from Rochdale that flips the Iron Works, and one for 1 pound from the market.
Use Shipyard card to build one in Liverpool that flips straight away, I believe. Total expenditure 27 sterling (25 from the shipyard, one from the iron and one from the coal).
Edit: change the prices for the shipyards, I forgot the coal. Total expenditure is 28 for the turn.