Steam-driven machines are less expensive than pump-driven machines but that is because they are lower quality and less durable.  Longevity and temperature issues are common complaints and these machines don't make true espresso because they don't create enough pressure. Most people will own one for only a brief period of time before replacing it with a pump-driven model.  You can find some steam models for under $50.00 but it is our opinion that it is worth it to spend more money and get a machine that will perform well and last a decent amount of time. Having said that, it might make a suitable learning machine for those who can't afford a pump-driven machine and don't make espresso every day.  It is also best for those who drink cappuccinos and lattes rather than straight espresso.

These machines have a small chamber where you put the water and then the machine heats the water and uses the resulting steam to force the water through the coffee grounds (which you've ground and tamped in a portafilter, just like the pump-driven machines).  The same steam is also used to froth milk.  There are few options available with these machines.  Some come with a glass carafe (which we don't recommend using on true espresso machines due to loss of crema and heat) and some might come with other accessories such as cups, but you can choose your model by brand name or by appearance as the machines themselves are pretty much the same.