I exclusively use the quad coils in my tfv4. It guzzles juice like crazy, but going through 15 or so ml a day of juice, i still get at least two weeks out of coils, my average is around 3 weeks, and I have had one last me 5 weeks. I use a juice that is basically crystal clear. Based on how long the coils last for me, I haven't really found any need to go to the RBA decks. Spending 3.50 every couple weeks on coils isn't that big a deal. I spend more than that on beer. The only time I have gotten less than two weeks out of a coil was when I was an idiot and didn't pay attention and vaped the tank dry and kept going and burned the cotton after 4 days. Totally my fault, so I don't count that one into my average.
As for cutting down on juice consumption, the tfv4 is kind of a bad tank to try. It is made to be a high powered, low ohm device. That pretty much always results in a lot of juice being used. If you are really concerned about it, you can try building a high ohm coil on the single rba deck and see what happens.