1. Can I get fit for the clubs I already have?
2. ^ Around how much would it cost?
3. What's the process of getting fit like? What all do you do?
A Fitting can vary from fitter to fitter. Most of the time you get what the above poster described. Some people fit statically, some fit dynamically.
Things to look for in a fitting-
Will you be hitting off of a lie board? This is the correct way to get your true lie angle.
How many combinations will the fitter use? The more the better. If they only have a few, then your really limited to what you even can be fit into. Some big companies have fitting carts with 50-200 options, while others like Henry Griffitts have up to 4000.
How long will it take? If they say it takes 15 Min's, I would find someone else.
Do they evaluate your swing, looking also at your current clubs? This is important to understand why you swing the way you do, if you need to correct anything before getting fit, and if you can adjust your old clubs...or get rid of them. A good fitter/teacher is ideal.
Will you be hitting indoor on a simulator or outdoor on a range, or both? If indoor on a simulator, you want to make sure its an accurate one. There are some out there that do not measure correctly, so it will give poor readings. You need to either have a very accurate Sim, or be on a range to test ball flight.Ideally both.
Will the clubs you will be hitting be the exact same specs as your receive? Check out the tolerances, they vary from each manufacturer.
Make sure you actually get to hit the clubs with all the combinations put together
Do they fit dynamically or statically? Should be the same price, but dynamic fitting is much more accurate.
Those are some key things to look for in a good fitting.
One thing to keep in mind is that there are a variety of deals you can find that will greatly reduce the cost of a fitting. Generally speaking, I've found simply asking for a reduction is useful. The economy isn't great at the moment and golf courses and shops are experiencing it. You should certainly take advantage of potential reduced prices by asking!
You definitely can get fitted for clubs you already own. I think that's what most people do. However, I think that if you buy new clubs, some places may give you a discount or even do it for you for a small fee. I think they cost about $100-$200 depending on the grab. I heard it helps a good amount in your game.