Possible Clues:

• Pair to perform at front of one church in rehearsal
• Cost to keep part of play in rehearsal
• Professional person's business
• Vincent perhaps takes part of play in rehearsal
• Fee includes something done in medical business
• 'The difference between ordinary and extraordinary,' per Vladimir Horowitz
• Doctor's business estimate covers what is witnessed in theatre
• Start to probe spasm in people? That's the doctor's business
• Drill
• The way things are done