A lot depends on how much you print. Epson rates their inks as being good for 2 years from the date of manufacture, or 6 months after they are opened. Many people report that the inks are good for significantly longer.
As a general rule, the larger the ink cart, the lower the price per ml. If your print a lot, the cost of ink is a major factor. If you print very little, the cost of the hardware is significant. If you don't print very much, you need to worry that a large ink cart might go bad long before it's used up.
If you print one or two 8x10s a week, then the 3880 may not be a good choice, as the inks will go bad long before you use them up. In this case I would recommend one of the new smaller printers.
If you print hundreds of 11 x 14's a week, you might want a printer with even cheaper ink (like the 4900). If your volume is high enough, you will save money by getting a 24" 7900, even if you never print larger than 8x10.
If your volume is somewhere in between, the Epson 3880 is an excellent choice. For many it is exactly the right balance of price, performance, and consumable cost.
