If you wonder if investing in a personal trainer is worth the price, I would have to say yes. Of course I am a personal trainer BUT when I go to the gym and watch some people lift weights or doing exercises all wrong, I just want to go up to them and correct them.
When you are just starting out in the gym, I would recommend you hire a personal trainer even if it is one session. If you are doing the exercise wrong, you could not only hurt yourself but you are not getting the benefits from the exercise.
Think before you lift and you will thank me :)