I was able to obtain a complete still in the box ink set for an Epson P900 printer, at no cost. I own and use the P800. THe box numbers are different and I'm assuming that my P800 would recognize and reject the P900 cartridges. I hate to give them away as they list for hundreds of dollars. Is there a way to use them in my P800, obviously without damaging anything.
You might be able to harvest the ink from the P900 tanks and refill the P800 ones. On YouTube there's a fellow, Jose Rodreguez, who has a lot about cartridge refilling. Here's one on the P800: