Contracts and Prices (Golden Rainbow)

Yes, under trade strategies, you can individually check each corporations salaries and change them, for my corporations that I contract to my own country or my other corporations, I sell at best price

This is especially handy to do with new corporations while they are upgrading, once you get the quality high, you may consider changing the trade strategy and selling on the world market, usually by this point you'll have some newer corporations to take it's place for selling cheap to your own country.