I don't want to make the issue more complex, but I will, for the sake of clarity.
Yes, spend hundreds more and you will get a "lighter" frame, be it aluminum or carbon fiber or whatever. Spend more than that and you will get lighter components that work a tiny bit better.
Be aware, however, that frame weight is "static weight." This means that it has very little effect on how well it will actually perform (except, possibly, psychologically).
You are a new rider but someone interested in fitness? Then get the best FITTING bike in your price range and don't worry so much about the rest. Best "fitting" means you feel comfortable on the bike, the bike feels comfortable holding you, you find it easy to control and aren't incurring pain to control it or ride it. You should feel comfortable riding it, bottom line.
If, after time, you become serious about racing, weight, etc., then worry about that then. Honestly, frame weight is relatively unimportant. More important, if you are considering weight, are the things you turn over and over and over again (i.e., "rotating weight") with each pedal stroke. This is the weight you actually feel as you ride and what can have an overall effect on your performance, speed-wise. this means wheels, cranks, and bottom bracket (the bearings which support your cranks). The best investment you can make to reduce weight and make the bike ride lighter are a sweet set of LIGHT wheels.
I know a lot of experienced framebuilders, including myself, who feel that losing 5 lbs off your body has a much more profound effect on your ability to ride quickly than a pound or two off frame/fork weight. They are pretty much the same thing in the sense that each is "static" weight that you carry with you every pedal stroke.
Anyway, I think this thread has made you think more than you intended and need to. best advice from someone who manufactures and sells bikes for a living is: find a shop where you feel comfortable and are treated respectably. Let them guide you. Trust your body as far as fit goes. When a bike feels good, you will know it. It may take a few weeks or months to determine that given your newness, but a good shop will support you along that path, and make changes as you discover what works for you.



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I hope I didn't either. From your reply, it just sounded like I made my point vaguely, if at all, so I wanted to try again.
