I have a epson 7800 , here,( in santiago, chile), there is a company that sells some clear plastic cartridges that you refill with some ink the sell you,
they say that since the cartridges dont have any foam inside you can fill them with up to 250 ml, the ink has no brand on the bottle other than their company logo, TIMG, they claim is just like epson ultrachrome..... the only thing I found was that the ink and cartridges are made in korea..... once you buy the empty cartridges, (about $ 60 each), the ink is dirt cheap, ( $ 25 for one pint).
here, original epson 220ml ink sells for $ 110..
this company TIMG is big down here on the small cartridge refilling bussines, but I have a $ 3.000 printer!
You will be completely undermining the integrity of your system by using other inks, and will be defeating the purpose of investing in this printer. As mentioned none of the Epson profiles will be of use anymore and just as importantly you will be losing all the support in terms of profiles available from Bill Atkinson, paper profiles for Epson printers from paper manufacturers, and compatibillity with just about everything else. You are right you have a $3,000 printer, and INK that is supported by more 3rd parties than any other printer in this price range. Short of taking a sledge hammer to it, using cheap ink in it is the next best way to make it worthless that I can think of.