We just had a set of 4 installed. Make sure to ask about extra costs like installation and materials. Ours were 23,500RD and we were told it included everything - except he may need to buy a cable - cost negliable. I was surprised when my final bill was 26,500 - 3000 extra for materials. Make sure to ask so that you don't get a surprise. Also if you have a computer it is cheaper just to install the monitoring program there than to buy a monitor.