Different kinds of yeast

I would like someone to explain the various forms of yeast which are sold and what different techniques are required to use them.

I am familiar with dried yeast granules and what we call here "Surebake Yeast".  Surebake is granules plus enzyme powders etc and this is what we always used in the bread maker machines.  I have been using it more recently for all sorts of breads and it does a very good job, but is expensive. 

I wonder, can I use another, cheaper form of yeast? instead of surebake and if so, what difference will it make in the final loaf ?

Thanks,

Paul.