Depending on the value of the house, I'd probably just use it as a negotiating point. If I was buying a $250k house, $2000 wouldn't really even blip my radar. If I was interested in it, I'd probably make an offer and say that I wanted the safe as well. If you balked, I'd just tell you to keep it. I wouldn't be willing to add to the buying price for it.

Of course, I'm the type of guy who would rather go out and pay $3600 for a new one as opposed to "financing" a used one for $2000 over 30 years (by incorporating it into the mortgage). In the long run, the extra interest wouldn't be worth it.

My first plan however, if I were you, would be to put it on Craigslist for $2000 obo and use the money towards closing costs. YMMV.