Looking online for places to buy some black gaff tape, I found this:
most expensive black gaffer tape
Amazon.com: 3M Black Gaffer Tape

At the list price of $1,402.98 for 60 yards, that’s $23.38/yard or $7.79/foot. Sure makes it seem like you’re getting a steal with the markdown, which makes it $0.43/yard (not including shipping, which adds another $5.92 for a price per yard of $0.53/yard).

Elsewhere on Amazon, Gorilla tape runs $10.94 for 35 yards, or $0.31/yard (not including shipping). 50 yards of Permacell Pro-Gaft Gaffer Tape runs $26.95 or $0.54/yard (or $0.71 when shipping is factored in).

If you need less, B&H has 30 yards of Delta Gaffer Tape for $17.50 or $0.58/yard (not including shipping).

I know there are places that specialize in this stuff for film crews. Anyone have any recommended suppliers of expendables?

UPDATE:
Thanks to the comment by Blayne below, I have some more price comparisons. Filmtools’ Permacel Pro-Gaft (they call it Cold Weather tape) is $20.80 ($0.42/yard assuming its the same one Amazon offers) and its Gorilla Tape is $8.98 for 35 yards or $0.26/yard.

Markertek has 60 yards of Permacel Cloth tape for $15.99 or $0.27/yard.

So unless the shipping costs at those places change the equation, it looks like film specialty places have gaffer tape significantly cheaper.