Local Markets vs. International Markets

There is a huge deficit of construction on KB. I have a few corporations that produce it, and two that use it. Is it always preferable for me to create local contracts and have my construction corporations sell to corporations that use it? It lowers the supply cost of the corporations that use it, but since there is such a shortage on the international market, the prices are high and my corporations that produce it will lose profit by selling internally at a lower price, right? So, is it worth it?

You'll get market price where ever you sell it. Local, Common Market, or Internationally. Local IS worth it.