I have to return to Jomtien Immigration at the end of June for my One year Visa Extension (I hope!) Will immigration charge me another 1900 Baht for this?

No you have already paid the application fee.

If you are waiting for your 1 year extension of stay based on marriage to a Thai to be approved, that's normal and you only have to pay the 1,900 baht fee once. Any other circumstances would require further clarification.

Edited June 17, 201016 yr by InterestedObserver