Great question — answering as the UphillTech team:
Assuming a new bike, look at the Scott Aspect 30, 20, or 10, depending on your budget. They all use the same frame, and the only difference is components. When you buy a bike with the intent to upgrade, realize you will spend far more long term, than if you bought your bike ready built with the same components you upgraded to. I understand why it can be better to do it that way to break up the cost, but it does cost a lot more money overall. I would make sure you buy a bike with good wheels, a good frame, and a good fork. Those parts are astronomically more expensive to upgrade to than to buy on the bike. Your budget is fairly low, so if you have the option, save a bit more before you buy....
Full answer by zenbike: https://bicycles.stackexchange.com/a/7719 (CC BY-SA 3.0).
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