Is there a recommended number of Botox treatments?

I've been really tempted to get Botox lately. How many sessions are typically required, and what are the recommended number and approximate costs? I assume the frequency varies depending on the area, such as for wrinkles or a square jaw, so I'd like to know how often injections are usually given and how many times a year is appropriate. I've heard concerns about resistance or side effects from getting them too frequently, so I'm curious about the actual treatment cycle. I'd also like to know if there is a significant price difference when booking multiple sessions together, and if there are differences in cost or duration of effect between domestic and imported Botox. I'm also curious about a budget to consider for my first time, as well as the duration of the results and overall satisfaction.