I have this printer. A lot of what your seeing has to do with the paper being used in my expirience, such as matt , semi gloss photo rag , museum etching and such. So far I like the printer, I print 8x10's but really use it for 13x19 prints on quality paper which I either mat , back and bag for sale or frame and mat for sale.
So far it has worked just fine for me. it uses 8 ink cartidges and you can view levels and replace as needed. On a conservative estimate I would say you get about 30 8x10's or about 10 13x19 prints for a 100 bucks worth of ink. I am still working on these figures as I print more materials.
Some inks get used much faster than others so it's really hard to judge. I suspect the number of prints to ink is much higher.
Things I have learned since buying the 9000. The 9000 uses dye based inks which for archival terms will fade faster than pigment based inks. I'm talking a ratio abnout 70 years vrs. 100 years. My next printer will have ink wells vrs. cartridges.
The casual printer can be more cost effective by having a lab print your photos. having your own printer allows you more latitude of control. I would think it costs more to print your own photos but I like having hands on control of what I do and my retail of my prints make up for the costs of printing them myself.
I hope this helps!