Updates to current website & making it fully responsive/scalable to any mobile device

We are looking to update our website www.cornerstonepresentations.co.uk, and also make it fully responsive/scalable to any mobile device (our previous developer was going to move it all into Wordpress for this to happen, so perhaps that's the best solution). Branding and look of the site will remain exactly as it is now, but we are adding some new content (e.g. forms, new pop up pages, new samples etc). Complete instructions are contained in the PowerPoint file attached, please ask if you have any further questions (we won't answer anything that's already answered within the attached file, so please read before asking anything).
We would like work on this job to begin wb Mon 6 October, and to be completed within 2 weeks. We will need to have a chat before work begins to ensure complete understanding of the brief, and we would expect developer to be reliable and communicate with us throughout process.
We're not sure what a job like this should cost - we've quoted a budget of £750 but don't know if job should cost more of less. So please provide us with your best fixed price for this job.
PLEASE NOTE: we will respond to proposals wb 22 Sep.