I don't think I would ever buy a bike off E-bay unless it was in my area and I could look at it and ride it. I just bought a 1998 520 off my local Craigslist for $550. It is in mint condition and came fully loaded. Actually, more than loaded because it had many pricey upgrades. The guy who brought it to the house also brought his Jamis. Nice, but not a Trek 520. Still, I would never pay $1,100 for a new 520. There are older bikes around like mine that are a far better value. True of any brand, not just a 520. Used bikes are cheap. Quality used bikes are a great resource.
You ask about expected repairs? For the average bike, I would be concerned only with BB integrity and whether the frame/fork was bent (look for 'buckling' in the paint on the tubes). You'll probably end up tossing the saddle and/or h'bars for something that fits you better anyway. Bottom line is: you're gonna fiddle with it no matter what. Normal bike repair is pretty inexpensive. A new BB on my Trek 830 was only $28 at the shop. A whole top-to-bottom tune is about $16.
Damage over 1500 miles. Under normal use, there should be none.