It's fairly common to make an upward move for the same or less money. When I was deputy of a large primary I earned much more than small school heads. The protocol is you apply for the job on the wage offered. It won't be able to be offered on mainscale or ups as it is a leadership role. Think of it as short term pain for long term gain. I can't think of many people I know who haven't been in this position at some point in their career.