How do different market structures affect the cost of trading?
Not very much. The three main kinds of market infrastructures are those with competing market makers, those based around order book that matches buyers and sellers and crossing systems. The characteristics that shape execution quality and the cost of trading tend to be liquidity and volatility. The latter tends to be determined by the type of security not the market structure, though arguably market maker structures may be more volatile in the very short term. Liquidity is not determined by market structure either. Therefore market structure does not really have any direct correlation with likely trading costs.
