Build a user friendly Website/Web App that creates project budgets

I am looking to create a website that allows users to create and administer Event Management budgets. The website should have the following functionality: - Sign up and create an account. A monthly recurring fee for using the website. - A web-app where the functionality to create budgets is held. o I have a spreadsheet currently that has most of the functionality that I would like to be put into this website, so it would be a case of using this as a basis. o But basically – the functions would be to:  ADD an Event to create a budget for (the user can create unlimited number of different Events)  Add SECTIONS of the budget  Add ITEMS to the budget – there is the client visible parts here where they just see unit cost and price, but then the user view where you see budgeted units and budgeted price  And then for each item, the user will be able to ADD PURCHASE ORDER for each individual item. This will then be tracked and a purchase order created. o There will be a ‘project summary’ screen for each budget where you can see the projected margin for the project and current spending level o There is the function to export a client friendly PDF of the budget o There is the function to export supplier friendly purchase orders. - There will also be an option to invite another user of the website to ‘collaborate’ on a budget so that multiple users can input and manage on the same budget - There will be a part of the website where users manage their account, upload their Company logo, address details etc that appears on the PDF budgets and purchase orders