This information is already in the public domain. The Department publishes the amount spent by schools on supply teaching staff and agency supply teaching staff (as well as costs and receipts from supply teacher insurance) annually for:
Local authority maintained schools on the Department’s School and College Performance website: https://www.gov.uk/school-performance-tables available for 2010-11 to 2016-17; and
Academies in the department’s Statistical First Release ‘Income and expenditure in academies in England’: https://www.gov.uk/government/collections/statistics-local-authority-school-finance-data#academy-spending available since 2011/12, when they were first collected in this format, up to 2015/16. Data for 2016/17 will published in the summer of 2018.