My opinion is that it is not that good deal. The seller is asking almost what the original bike cost if not more.

I will also say that a lot depends on the condition of the bike itself. Things that may or may not need replacement for an older bike may be

Brakes or brake pads
Cables and cable housings
Tires,
Chain

This can start adding up quickly and if it reaches the $800-$900 range, you probably can get a newer used bike. I may pay that price if there's no work involved and the cosmetics were in great condition, but only $300-$$400 if it needs a lot of work.