Do you know when you were hacked? When was the last time you saw it prior to being hacked? You might be able to get away with restoring a backup then hunting for the security breach. Often the actual hacking will have occurred months prior to any noticeable changes.
I would start with taking an immediate backup of your site. So you can compare files to a previous backup if need be. I would then Google something along the lines of “WordPress hack recovery checklist”, it should turn up some good results. Pay special attention to any bits about removing unauthorized accounts, and resetting passwords. Typically they leave a way to get back in. You don’t want any loose ends.
Also, remember to update your site. To this date I haven’t had a site hacked since WordPress imitated the one click updating.
