Ports have a random STARTING price but they can go very, very high as there isn't a real upper limit. As long as a port isn't traded the prices will go up.
There ARE a few fixed price ports but those won't be created when you build a port.
And a port will bring you profit when you trade with it.
That will be the only profit you can expect from the port. Most people will only be building ports in SG sectors to help them defend or get planets started.