Web App Developer

I need a web application created for a property investment calculation tool I am currently developing.
The product itself is designed to make property investment easier by giving investors a real time, accurate and reliable projection of their potential returns on investment over a given period of time.
There are currently similar tools on the web but none are as accurate and valuable as the product that we are creating.
I am looking for a user friendly, accessible and professional web app that is inkeeping with the brand image created through our website (www.palc.co.uk).
Initially we are looking to have a current calculator reverse engineered and then altered to suit the UK market as opposed to the US market. This calculator can be found at: http://www.nytimes.com/interactive/2014/upshot/buy-rent-calculator.html?_r=0.
This calculator has several features that we are looking to incorporate into our calculator but of course there are different features we want to add to suit our market. I have an in-depth product development design brief that I can send, as well as an excel calculator that I have created with all the features that will be present in the app built in which I can also send if you are interested in working on this project.
The budget is also relatively flexible depending on the estimation of how long the project is likely to take.