Our advice
Keeping track of costs in Excel: update

To get users to adopt a tool, whether Excel or not, there's a confidence-building phase. Users will try to test the tool, to see if they find any errors, to reassure themselves. In this respect, one of the simplest tests is to check whether the realization data fed into the tool matches that of the information system(s).

So, before deploying your tool, make sure that the realization data is 100% reliable, even if it means losing time in the roll-out. Otherwise, you run the risk of negative feedback on your tool, or even rejection by users, before they've even had a chance to discover its benefits.