If your work is 99% b&w then your question is almost answered...
consider the extra cost just for the 1% of work, the prices for laser
toners aren't exactly cheap and there's more than one to replace.
I am on my 2nd mono Samsung laser, the first one a ML1510 had been
refilled and refilled till the drum gave up... this produced PCB circuit
design as well as text so it did have some 'clobber' and refilling was
like 'shelling peas'.
The replacement is a ML3050... and in both cases the price of the toner
is about as much as a new printer especially the ML1510, how easy this
will be to refill I can't say but if you want a refilling idea to see
which is the easiest have a peep at 'Refill toner UK | Toner refill your
empty laser printer cartridge | U Refill Toner Ltd.'
(
http://www.refilltoner.com/) also gives you insight how it's all done.
davy