Digital BW, The Print

Hi guys :)

I'm still trying to figure out a plan for getting myself set up for
hextone printing. (Was trying to convince myself that it was possible
to make good BW prints from my 2000p but it's just not happening.) 

My question now - how many cartridges do you need to go through before
it's sensible to have a CIS instead? 

The CIS for the 1280 costs $225 as opposed to the much less expensive
version for non-chipped printers (presumably because the custom chips
cost them a lot to develop, which is only fair.) So presumably if it
can replace 5 sets of cartridges (at $25 each or $50 per pair) it's
well worth it. Are inks that much cheaper in bulk rather than
cartridges that the CIS pays off quickly? Or do you need to do very
high volume printing in order to justify it? 

Right now on my 2000p (using epson cartridges) I figure it costs me
around $1-$1.50 per 8x10 print for ink. How does that compare to
per-print costs using the MIS VM inks through a CIS?