This simple answer to this is two, that is really all you need. One for Theatrical, and one for Commercial. Or too make this even more simple, one with a smile on your face, and one with a concerned look on your face… Smile - Commercial, Concerned look - Theatrical.
One bit of advice that I was given early on is this: As an actor you should never choose your own head shot. Why? You are typically your own worst critic, and others that are more qualified to do this job, like your agent or manager. Some photographers say to take your favorite five and show them to everyone you know, and make a choice that way. NO! unless you have no agent or manager, then this would be your best approach.
Taking your new proof sheet to your agent or manager is a great thing, and it gets them involved and excited about promoting you, and getting you work. Telling them I want to use this one, and not that one… is not productive… if they are any good at getting people work, they for sure know more about what photo will work than will not. This is what they do for a living. You are an actor, not a head shot selection person. Do your job, and let the others do their job.
I would say that getting new head shots once per year, is about the right thing to do. If you are a kid, every six months…
You should spend between $350 - $500 for quality shots. Remember, it costs money to make money, and your head shot is about the only thing most casting directors will see of you in the start of your endeavor. Its your calling card as an actor, it is VERY IMPORTANT that they work well, and all that means is when you, your agent or manager, send them to people, those people call you in for an audition. The rest is up to you.
If your Head Shots are not good, you will not get auditions.
Also remember that you want to look like your head shot when you roll in for your audition. This means do not over do the makeup, or whatever… look natural, and look like you do in real life.
I have personally helped in casting, and have been amazed at how different people look from their head shots, so much so… that after an audition they just get tossed in the “Rejected” pile… for not looking quite right for the part.
I hope this helps, and remember to check out this web site for a ton more information on this topic. Head Shots 101 !!!
Have fun, and enjoy yourself… life is too short to not have fun!!!