Hey there,
I actually did some prototyping of this kind in college and had a lot of fun with it. Usability and UX is something I studied extensively.
Firstly what I'd like to do is have a skype meeting with you and sort out exactly what kind of features you want to see on your website and we'll work out as many use-cases as possible. Then we'd move on to doing a paper prototype that I could demo. We could fine-tune what we want to see from there.
Once that's done we could use software to do an interactive prototype that demos how all the features would work. And I'd be working closely with you every step to make sure you get what you're looking for, but also giving you my expert advice on how the enduser will experience the app. I'm asking for the maximum bid because I want to be able to give you as much time as possible to do this one right.
This kind of work is probably as fun as computer science can be, so if you want a great product that reflects passion for the work, I can only encourage you to hire me.
Feel free to contact me with any questions or concerns. I'm happy to talk on skype or on the phone to clarify anything you might be asking about.