If "ordinary" 8mm Sony tapes (as opposed to "data grade" ones)
are OK (I've used them for years, without incident, though the
collected folk wisdom advises otherwise), Honest Ed's is a good
source.  Last time I bought them they were around $7 each, lots
cheaper than other standard sources.  (I've occasionally found
them even cheaper at various fly-by-night places on Spadina.)

Of course, our drive is an old 8200; dunno how they'd work in
the higher-density drives.