User tabular data entry to build a budget worksheet?
You could try https://drupal.org/project/tablefield or https://drupal.org/project/slickgrid
From module page:

The Slickgrid module is an implementation of Michael Leibman's jquery slickgrid plugin, a lightening fast JavaScript grid/spreadsheet.
It defines a slickgrid view style, so all data can be output as an editable grid.
This module will only work with Slickgrid 2.1.

These do not provide spreadsheet functionality, but you would probably implement the summation or whatever calculation is necessary.