There is a difference between a pro fit and being put on the right size bike. Any decent LBS will get you set up on the right size bike as part of the sale. A pro fit takes things much further and may or may not really help/be necessary.

Also, keep in mind that the $200 savings does come at a price. You will get no warranty and little support without paying for it. This may not be a huge issue if you are an able bike mechanic. Even then, if a frame fails (unlikely, but possible), or you have trouble with maintenance, you could be ringing up a bill higher than $200. Not saying used is bad, but you really need to know what you are looking at and how to deal with anything that comes up. Most beginners are not in that kind of position.

I also would not pay $6-700 for a 7, almost 8 year old non-vintage bike. If it were me and I were a beginner, and I could afford it, I would really try to find a good LBS that will help get me into a bike that will suit my needs and support me. Not every town has an LBS like that, but it is the ideal situation.

Almost forgot, don't get hung on the component names. Anything that the big 3 put out these days is going to perform well. Even the newest Sora looks pretty decent, and Tiagra is about level with 105 at the moment. So don't let the name on the derailleur sway you too much.