Create a website front end with logins for an Excel spreadsheet of prices

UK based hourlies only please

If I get the go-ahead this project will be time critical and will need to be completed asap.

Previous examples of your work relevant to this requirement would be appreciated- I think you will need a good grasp of both Excel and web based databases to be able to help me.

In short I have a vast Excel spreadsheet of prices for the products I sell- with various parameters which can change the price.
I need a web based front end that can manipulate the data I have by use of tick boxes etc to allow my clients to access this website (and ultimately my pricing data) using their own login so they can accuratley quote for the products themselves and save me time.
I need the ability to upload my data in excel format to the site as and when I change it, as well as to control who uses the site, add and remove them as required.
I have a full specification with screenshots written which I can send over.
I will also need you to be available for future upgrades and improvements in the longer term.