Secondly, you really need to learn some math. INKJET printers, even the cheap Kodak printers, still run at MINIMUM 10cents per page black, 24cents per page color. LASER products range from 1cent - 4 cents per page black, and 6cents-10cents per page color.
Thirdly, if your machine DOES for some reason only get 2800 pages from a "$700" cartridge, and you say you are saving "$3000 per month" by refilling, then you OBVIOUSLY did not do your homework on the equipment you were buying, or you would have realized that with THAT type of volume, that machine is WAY to small for your needs. These things have monthly volume limits (and although they are only guidelines, not set-in-stone amounts, drastic overages WILL destroy the machine). Saving $3000 per month by spending $20 rather than $700, you are effectively saving $680 each time. $3000/$680=4.5 sets of cartridges per month. 4.5 sets x 2800 pages per set=12352 prints per month. If a full set of cartridges costs $700, then you can't have anything much bigger than a desktop machine, which are only rated for 3000-5000 pages per month.
If, as a business owner, you can't see this, then you deserve to be losing money.
Also, what kind of business has their fax machine connected to a main voice line?