I have a Cannondale F400. At the time I bought it at full price, ~$800 I think, it was somewhere in the low-middle end of C's lineup. I am not sure about Cannondales current offerings. It has a fantastically light, yet sturdy frame that is/was carried up the Cannondale line, albeit with better components. I am relatively light (5'9", 150lbs) but don't mind the stiiffness of aluminum. It is so light, I can pick it up with one hand without even thinking. This is no small consideration when you are biking up a steep hill, or after a day on the trails and you have to load it onto a car rack/pickup bed/van/up several flights of stairs.
Other manufacturers have decent offerings as well. But they usually have the design philosphy of keeping all of the components at the same level. That's fine too. I personally have never regreted investing more in the base frame with the potential to upgrade the individual components later if I wished. Barring any breakage, I will probably have it for life (although titanium frames do have a certain allure).
If you are going to be changing tires frequently (or at all), I suggest getting a model with quick release hubs on the front AND back (not always present on lower priced models). I absolutely agree that it should be properly sized by a knowledgable bike shop tech. Find one locally that you trust (and ideally is within walking distance
. Lastly, I instruct you with all of my might to get a good fitting helmet, and WEAR IT! No joke.
Good luck on your future purchase.