The Department of Administration released its statutorily-required report on contract services in December 2018. You can read the report here. Or, to see a one-page summary, you can look at the chart we created using DOA's data here.
There's another interesting report that DOA released recently. It's called the State of Wisconsin Classified Workforce & Affirmative Action Report for Fiscal Years 2015 and 2016 which can be found here. It includes a chart showing separations from state service during the years fiscal year 2004 to fiscal year 2016. You can see a scan of that chart here.
A couple of interesting things start to happen around 2011. The money spent on contract employees increases greatly while the number of state employees separting from state service also increases a lot.