What recourse do I have if the prosecutor handling a case delines to prosecute?

If you're talking about an assistant DA (ADA), you can go his/her boss--either a high-level ADA, or even all the way up to the District Attorney. If his or her boss(es) won't overrule and require prosecution, then effectively all you can do is to go to an elected official--mayor, councilman, etc.--and see if they will put pressure on the person to prosecute. However, at the end of the day, unless you believe there is criminal activity (e.g. a bribe) or a serious conflict of interest (e.g. the prosecutor is related to, in business with, friends with) the suspect--either of which would be grounds to go to the state Attorney General's office--there is little you can do if  the prosecutor simply won't prosecute; "prosecutorial  discretion" gives them the right to exercise discretion in when to prosecute and when to not.

Of course, if you suffered physical or monetary injury, property damage, etc., you could sue the suspect in a civil case, though if the suspect likely doesn't have the resources to pay a judgment, this may not help. (Think OJ: he was prosecuted but acquitted; however, in addition to that, the victims' families brought a lawsuit against him. If there's grounds for a suit, you can sue regardless of what happens with criminal charges.)