I use Seachem exclusively. I run it for 2-3 days per month in a cheapo HOB filter in my sump. Seems to work for me. I think a $19 purchase last me a year or so. I don't really track my costs. If my wife ever found that info.....I'd be dead.
I use Seachem Matrix carbon and TLF's Hydrocarbon only. When I'm not slacking off, I change the carbon every other week. I buy the large bucket packaging and it's fairly economical. I don't spend more then $30 or $40 a year.
I always have Black Diamond on hand to use in an emergency with a Magnum HOT canister filter. I usually don't have to run AC on my reef tanks, but do in my FOWLR tanks. When I do run it I change it every week.
I use a whisper 60 on the 90 reef (which is connected to the 150 through the sump) and they use their 7Acre carbon in the bags. I try and change it out every two weeks or so which is probably too long. I can get 12 whisper refills on-line for about $10, the whisper takes two at a time, so I get about 12 weeks out of that $10 plus some mechanical filtration.