You stated that you are bushing your teeth two to three times a day.  That you also floss at least two times a day and you are useing Listerine mouthwash after brushing, as well as seeing your dentist for the required cleaning.

I think you are covering all your bases very well. There is not much more you can do. I know that there are some mouthwash that will indicate that they have gingivitis protection maybe look for that. I have hear of the Oragel Mouthwash. My friend uses it sometimes and it does work for minor mouth pain.

There is not enough information given in order to give you a more accurate idea of cost. Rates depend on your state that you live in. Do you have dental insurance? If you have dental insurance or a plan this a course would save you some money.

The type of cleaning that is normally done for gingivitis is what we would call a deep cleaning. A dental term would be gingivectomy and generally charge per quadrant (you have four quadrants in your mouth)

A rage of cost can be any where from $100.00 or more per quadrant.

to get a more accurate state range you can go to
http://www.insurancecompany.com Just key in you zip code.

You will want to brush normally, though you may want a soft bristle brush. Also do not forget to floss every time after eating. There are also mouthwash that you can use for gingivitis so look for them. Then finally do not forget to see your dentist. They may recommend that you get a deep cleaning.