Hi,
Last year I had all windows replaced in the house, which meant re-connection of sensors & in some cases replacement sensors... was originally quoted €290, but after alarm company guy did the work, there wasn't the expected work he thought and charged just under €200 (existing wiring to sensors didn't need replacement)... I don't have monitoring as part of the alarm.
€540 for reconnecting the sensors / new sensors seems, to me, a bit high. How many sensors have you internally? is there other work besides reconnecting the sensors that need to be done?