I am looking to buy a bike for Fitness purposes and need advice. I ride 20-30 miles 3 to 4 times a week and occassionally up to 60 miles. I currently am riding a $200 Mountain bike with fat slicks. The bike is heavy and the lack of hand positions hurts my hands on longer rides and later in riding season. I ride on asphalt trails and roads which are not always smooth so strong rims are essential. As well I don't want to kill my back by being bent over too much + I want to see around me not just the asphalt beneath me, nor do I want to rattle my bones on 700x23 tires(I think 700x28 would be fine) so a balance of comfort (perhaps carbon forks & seatpost) and speed (I like going fast and I like climbing hills so its gotta do those things well) I would prefer to buy used (not too old) with decent durable components (like Shimano 105's) and am looking to spend around $500-700 on it. Any suggestions on A) Brands/Models & years?
B) where to look to get the best deals? (I could buy in Canada or the US)