I charge $500/day for long, multi-day trips; $600 for shorter durations as SIC. I also charge by calendar day, not 24-hour period, i.e, if the flight leaves at 10pm on Wed and returns at noon on Thurs, that's 2 days. In addition to the daily rate, all expenses are covered.
Our dept rarely uses contract pilots but we pay $600/day + expenses. We're based in SoCal.