Digital BW, The Print

Would someone who knows be so kind as to let us know what to expect in costs when 
switching from color to black and white printing on the 4800?  I've read posts that state 
that 94ml of ink is used when changing over.  The ink costs for a 220 ml cartridge is 
about $90.00 so if we use 94ml in the change-over, we would consume about $38.00 
each time we switched.  So if one is printing color and wants to print some B@W and then 
return to Color, he would have to lose about $76.00!  Am I perceiving this correctly?  
Joe Davajon