Mockup website and user interface talented designer

We need someone to create the mockups and the user interface of a questions site, a social bookmarks site, a personal file storage site and an activities site. The basic design is already made so mainly the user interface is what is needed. We don't need PSD files or anything that good but simple designs and advice on fonts and sizes. We don't want to overcome budget so if it's not enough, please do not bid.