Hi. I'm helping someone sort this out at the moment! I called their local private olive mill at El Perello and the chap was quite helpful. He told me that the minimum quantity required for pressing was 300 kilos and the cost would be 75 euros for this quantity. The only thing I couldn't manage to get out of him was whether you need to reserve a slot so he is probably going to pop in and ask him in person. I have seen the mill at Aldover so perhaps you could go in yourselves before you harvest and ask them. Be aware that there is a minimum quantity of olives that they will press. If you need any more help just ask as lots of people using this forum are harvesting their olives around this time.