Lisa, my experience with the 6300 is that it is quite a frugal printer (if you can call any printer frugal). The cleaning cycles are mostly done in the background so I have rarely been aware of any clogs - in fact my previous 6100 performed faultlessly over four years and much use. When I change the maintenance trays they held about 450ml of ink - which is quite a bit, though that was over a year or more of quite heavy printing. I am assuming your printer came with 330ml cartridges, because the 6300 comes with 90ml starter kits, and then the normal cartridges are 130ml. And as I said earlier a lot of ink will have been sucked into the feeder lines when you first installed the heads - though of course this will not need to be done again.
Overall I would not consider any of these printers suitable for occasional use. Mine is used most days - sometimes for one small print, other times printing non-stop for several hours. They are surely not designed to be left off most of the time, and then fired up for one-off jobs. I am sure they will do a huge amount of head cleaning in this case and you could easily use more ink for cleaning than for printing.