Transform Excel to WebPortal

Hello fellow OS guru's :)

I'm looking for a way to transform / build a webportal based on an excel document.
So basically this is a sheet with input/results which would be on the webfacing side, and a calculation sheet which provides the results for the front. In the calculation sheet there are numerous values and calculation rules. In excel this is all pretty dynamic and can be changed on the fly.
But when making this a server side thing, with some backoffice Form or Configuration screen, the business user loses the flexibility to change his calculation rules if I make all this too static.
So the goal is give the customer/client the web facing form, he fills out the nessecary fields and submits it.The backoffice must have a screen with the calculation values and rules. This should be as dynamic as possible, there is always a new parameter or changing value. I guess one could call this a 'pricing module'? 

So how would one approach this.

Thanks for your input!

Hi Patrice,

There's no easy way to allow configuring actual formulas in the backoffice.

Also, in theory such configurability seems nice, but in practice it's a nightmare waiting to happen, as you basically give the business a tool for changing the software behaviour.