There are lots of sites dedicated to DIY C02 lasers up to 50 Watts.

I want to find out about the industrial type lasers between 1000 and 1500 watts.

What is in them, that makes them so expensive ?
How are they constructed ?
What sort of duty life can I expect out of these lasers?

I have done some seriuos googling but never seem to find out much about the higher powered ones.

So far all I have found out is the higher powered lasers are pressure filled with CO2 unlike the lesser powered ones been vacuum filled with thinned out CO2.

The higher powered ones are gas assisted. ( Oxygen and other gasses are streamed onto the cut to assist with cutting)

Does any one know of some links that may help me?

1,000 and 1,500 watts?

Asked what you do need this laser to make to apply? The metal cuts?
This is the price many, the use space and the maintenance are many,
suggested you use the water or the plasma. Such economy and the very
good maintenance is convenient.