Building Custom Budget Adjustment Dashboard

We're looking to build a custom page that would allow users to simply enter adjustments to project budgets during the year and to check their changes for errors on the fly. What we imagine is a page where a user enters the business unit and project id, then hits as push-button that populates existing values in the database into a grid. They would then be able to make adjustments in a custom field and would be shown a new, calculated total for that row. They'd also be able to add rows altogether. Once they are satisfied, they would save the