How much does a Land Rover Discovery II coolant system cost?

There is a 2000 Land Rover Discovery Series II I am interested in buying. The people are asking $4,000 for it and they say that I will need to replace the coolant system. So, my question is, how much will it cost to replace? I have a cousin that would replace it for me for free, so all I need to know is how much the coolant system itself would cost. Thank you very much for your help. =)|||Try to find another discovery, i bet less than 1,000.|||The entire system?