Actually, yeah, my math was way off lol, it's more like $1 worth of ink, but definitely not £1.85 though, that might be because the R2880 is a small-format printer... The big 200ml cartridges cost about $950 for a full set vs. $95 for a 2880 set, but even though they are 10x the price, they hold 20x the volume of ink, so twice as cheap. The x900 series of printers also use up to 10% less ink per sq. inch than the older x880 printers.
To produce a fully framed and matted print ready for sale works out just under £16.50.
Could be more, depending on the matting and frame used, but if you sell a print that cost £16.50 to make for over £100 you'll be getting at least some money back. But that depends on things like how much of a pretentious snob you are, local market, etc. For an especially large print, in a very nice frame, I could probably get away with charging $500 for that. Some photographers charge thousands because of good marketing.