4900 vs D3000 Mini Lab
Your 3880 should be producing a log of each print job and the amount of ink used from each cartridge to the nearest 0.01 ml. The job log is exportable as a CVS fike which can be analysed in any spreadsheet software. Paper costs are easy to estimate.
Looks like Red River Paper has already done this and the cost of an 8x10 comes in at under $.50 with Epson Premium Luster. Roll paper with a 4900 and the higher capacity inks should bring this down further.
The savings will take some time to pay for the printer, so I'll wait until the next $500 instant rebate to help with that a little. -Possibly sell the 3880 on Craigslist to also offset that.