In the 2 years I've had the Pro-1000, I've used 55 ink cartridges (at 80ml) and 7 maintenance cartridges (at 220ml--thank you Panagiotis). That means 35% of the ink has gone to the maintenance cartridges.
I print almost every week, usually more than once, I never print borderless, the nozzle checks have been flawless so I've done cleanings maybe once, I always leave the power on...
My Epson 3880 (second location) has used 2 maintenance tanks (unknown capacity) for 48 ink cartridges, even with not infrequent ink swaps. For last 2 years, often sits weeks unused, and I've done cleanings only about 3 times in 6 years.
I've just replaced the Pro-1000 with a P5000. Powerful roll capability and hopefully lower ink cost (40% lower $ per ml, and hopefully lower self-consumption).