How much room do you have to negotiate a salary offer?

I was expeciting a much higher offer than I got. I asked the recruiter if we could go back and ask for $5k more per year (hoping that maybe I'd get 3k from it). She was very skeptical and she is trying to get me to promise to take the job if she goes and asked for more money. I flat out refused to promise to take an offer without even seeing it. I'm very turned off by the whole thing and thinking about just walking away. Is it unreasonable of me to expect some negotiation from them?