What should this bike cost??

Ballpark??

$600-900... but it all depends on the condition.

Before you even start asking questions of the seller, ask yourself this first... does it fit YOU?

Mavic Cosmic are basically very sturdy (and very heavy) aluminum wheels, that are really not that aerodynamic (they look the part though). As training wheels, they're great!

Things you should ask:
How many miles on the components?
Is the steerer tube cut, if so, how much room is left for upward movement? (unless you know that you need the stem to be slammed)
What kind of maintenance/cleaning has been done?
Has the bike been crashed (could be the reason why the components were replaced...)?
Is the seller the original owner? (if not, you basically have no idea how the first owner treated the bike...)

Then you need to take a very close look at the bike. There should be no dents and no major scratches (a bike from 2007 will have some superficial scratches, but as long as it's not through the paint, you'' be fine). Look at the components, especially the wear parts (cassette, chainrings, chain, brake pads), they may show signs of wear, which is ok, but not excessive wear (which is an indication that it may not have been properly maintained).

I'd guess around $1100. That's a solid bike. I did a quick search and I think his asking price is too high. If you're adding up the cost of the parts, I would assume that the seller didn't purchase the Rival components new at retail, but rather they came off another bike he purchased. I'd estimate something like $350 frame, $650 components, $200 wheels. And I guess I need a -$100 one year of use depreciation in there, too.