Is the $79 (+20) just for the exam or does it include glasses ? How much are bifocals?

Exam only, other is extra. The +20 gives you 3yrs worth of exams in 6 mo intervals instead of a one time exam.

In all honesty your bill, with glasses will probably run you around $250. With the exam, buy one get one frames, and then there's the cost of your lenses. Depending on what features you want for your lenses, they can get spendy.