All the beer distributors in my area (Northeast PA) either fill them or swap. 17 is kind of high, I pay 6 to fill or 12 to swap. Call around to your local distributors, I'm sure they do the same in your area.
I remove the valves every other beer and give them a good cleaning and then sanitize and lube. When I don't do that I just fill the keg with hot water and run it through the lines followed by oxy and then finally starsan. Never had a problem doing it this way.
I am going to be doing my first soda and have a couple questions.
Do I need a dedicated keg for sodas?
Can I for go the yeast and force carb just like a beer?
If I have my already carbonated kegs set at serving pressure for an extended period of time, do I have to worry about them absorbing more CO2 and becoming over carbonated