Anything inkjet by HP would eat you out of house and home.
At that printing volume I would be looking at a Canon ip3000, ip 4000, or ip5000. ---not the new Canon's with the chips-----then find a good third party cartrdige seller or refill. You can easily get your
B/w text costs to below a penny a page.----including the .5 cents for paper.
And considering you can still get a pixma ip4000 for about a $100 while they last, thats what I would be looking at.-------or spend $200 for the MP780 which prints copies scans and faxes for $200. at office max----with a printer engine from the ip4000.
For what its worth, I use cartridges from
www.bulkinkjetcarts.com but other good suppliers exist.
And I bought my wife a pixma ip4000 and me a used Canon mp730 so at least I put my own money where my mouth is.