The spreadsheet is more accurately called a 'workbook' and it can contain as many 'worksheets' (tabs) as you need. You could create a worksheet for each contractor and on that sheet include the 'money given' and 'Expenses incurred' with a reference to the 'Site' it was spent on.
In this way each contractor's finance is kept separate but, if you want to keep a total of the 'money given' by yourself, then create a worksheet for yourself and reference the 'money given' totals in the other tabs.