You can price the items at the Store on Apple's website.
iMac, MacBook Pro and Mac Pro machines will all run Final Cut Studio, what is your budget and what level of professional are you talking about? You'll also need external extra hardware including at least FW400 external drives (or extra internal hard drives if you select the MacPro). Something to monitor audio. If you mean "professional" some way to monitor your video in a professional external video monitor (as opposed to the computer monitor).
If you asking this question are you really sure you have the skills to start up a business as a professional or would it be wiser to spend some of your budget learning the trade and then when you have the knowledge then go out on your own?