I don't know prices where you're at, but here's some info that worked for me...
buy a steel bike in your price range, worry about the frame and fit only. Don't worry about components. I don't think Shimano Tiagra is that much better than Shimano Sora, so don't waste your money on Tiagra. Just upgrade components to 105 or Ultegra as they fail. Even if your wheels don't fail, I'd spend the money on a better set before your 1000 mile ride, perhaps Mavic Open Pros with Ultegra hubs... but that's down the line.
You don't have enough budget for a quality fitting, but the shop you buy from should give you a basic fitting, a good start. As such, you should learn as much about it yourself and tweak one thing at a time until you get your bike comfortable enough. Check out
http://peterwhitecycles.com/fitting.htm and google for more info. Learn as much about fitting as you can as well as basic bike maintenance.
Does 500 include pedals and saddle? cheap bikes usually come with horrible saddles. Is the 500 also supposed to cover helmet and other cycling stuff like clothes, frame pump, on-bike tool kit, spare tube? I know they're goofy, but I strongly recommend lycra bike shorts. Perhaps make the jump straight into bib shorts?
What's this monster ride you're doing?