How easy would it be and what would it cost for the "normal"man in the street to hire a small film crew?

Well, how small are you talking about? With the technology available today you can start with a crew of 1 (or 2), you and your video camera and move up from there. You would probably need at a minimum a camera operator/cinematographer and a sound person. And one thing about filmmaking is that time actually is money so how much it might cost you is going to depend on how long you need them. And the cost of hiring professionals is going to absolutely vary depending on where you live and the level of professionalism you want.

You could check with the local colleges and see if they have film students that are willing to work with you for free. I would think that the cost of hiring professionals would be prohibitive. You might also be able to rent some of the equipment. You might want to check with a copywrite lawyer before you dive into deeply to find out how to protect your ideas before someone else takes them as their own.