Short online video - event promotion

We are London based small company and are looking to put together 2-4 min long online promotional video for a single educational event.

We would like quotes for the following:

Green screen video shoot + professional editing
- Two people talking, extra graphics to be added to final video. Total length of video 2 - 4 min.
- we would need couple of hours for video shooting
- venue for shooting provided, all equipment required incl lights, green screen etc.

The job will need to be done in December 2012.

Thanks in advance.