For a monopolist there is no going market price. He sets his own price which is a consequence of his own actions. In other words, price is the effect and quantity supplied is the cause as opposed to perfect competition. The welfare consequences of monopoly can be analyzed by making use of the concept of consumer and producers surplus.
Monopoly reduces the consumer surplus and increases the producers surplus.
In addition it also produces a dead weight loss. However, it is hard to figure out the size of a subsidy and also there might be some opposition to generate political support for subsidies to the monopolist. Another way to pursue a monopolist to charge competitive price is the price ceilings. Again, it is difficult to determine the exact size of price ceilings. However, there are some problems associated with regulating a monopoly.