Don't know how expensive it really is, but if you live in a farming area ask a farmer if he has any graphite left over from planting season. Alot/most planters now use talc or graphite as an actual seed lubricant and they go through the stuff by the boxes!!! Give 'em a couple bucks for a 1# canister of it and you'll be set for life...not to mention you find all sorts of uses for dry lubricant around the house.

I guess you could halve pencils and grind them up too...if you're board