Design UI for Mobile/Web site

Looking to have a simple and clean UI designed for a video site I am currently developing. On top of the actual graphics design I'm looking for someone with experience in creating the actual logic and placement of different elements to make search, navigation and general usability very easy for users. Please note this is an adult themed site, so before submitting make sure you are fine working on that. The sites main focus is mobile, but it does have a desktop version. The site basically allows users to embed videos hosted on other sites. These videos are then viewed by other users who then categorize the video based on a number of variables. Once a video reaches a certain amount of the same categorizations for the same variable, that category becomes locked. Users can use a filter menu to search videos based on as many or as few categories as they'd like. Right now the site has about 35 categories. I would like a clean and simple way to choose category values from a slide out menu on the mobile site. Also looking to create a good way for users to assign values to videos after watching them. From this brief description can you give me a ball park figure as to the cost? Thanks.