You are missing something: how much is spent because the spreadsheet isn't the right solution - nobody measures this (or even knows how). How much are you risking because spreadsheets are not robust - when will a mistake catch up, and what will be the cost? There is a reason accountants use double entry bookkeeping, and spreadsheets don't have that.

Nobody has the money to spend doing things right unless they have been burned. That doesn't mean the money shouldn't be spent first.

Spreadsheets are powerful I will grant. However they are not robust. A robust system works very different and includes features (like tests) that your spreadsheet doesn't have (I don't if it could have them, but it is safe to guess they don't)