If they have the money for a bus, they have money for the overtime bill. Last I heard it was around $250K.
According to the FDLE:
As of 8/13/13
Daily Estimated Costs and Incident Reports for Capitol Protests
Estimated Costs*
Overall Total- $413,822.35
Overall OT Total - $149,998.30
Total for 8/13/13 - $12,667.28
*Includes regular time and overtime.