Why per-person pricing works
A single event price needs recalculating whenever ten guests are added or removed. Per-person pricing means changing one quantity and makes the cost of an extra guest clear. Keep equipment hire, setup, transport and hourly staffing on separate lines. This also explains why a smaller group is not proportionately cheaper.
State the deadline for changing guest numbers in your quote, for example seven days before the event. After that, invoice the agreed minimum even if fewer people attend.
