I too am guessing you mean the 2531.80, but correct us if we're wrong!
It's an absolutely outstanding watch---at 41mm, the best size and form-factor the 300m diver has ever had, IMO. Nice and thin, too, with a substantial bracelet.
That said, do NOT buy one until you've done some homework---and better yet, uploaded detailed pics from the seller
here, for us to review. This has to be one of the most commonly faked Omegas out there. The odds of buying a bogus one are relatively high.
Know that it's not a rare piece: there are many of them out there to be found. (On Chrono24---even after filtering to include only those that are actually "in stock," there are 73 ready to go.) That means you can take your time and find one that's authentic and in good condition---perhaps even with a recent service, which adds real value! Box and papers... for what? The watch will be way past the warranty period, so the papers aren't worth anything, nor is the box. Some folks seem to think that having these items makes the watch more likely to be authentic, but that's untrue: anyone can buy boxes and papers after the fact on eBay to make a "full set." For a rare, collectible watch, sure, it could be compelling to have those things, but this was a run-of-the-mill mass-produced Omega. I'd put
way more emphasis on finding one in good condition and with a recent service. (Make sure it includes all the links you'll need to fit your wrist, too---always pays to read the fine print in the ad.)
Let us help you! What country are you located in? What's your budget?