If you take old documents to an outfit such as shred-it.com, note how they calculate their charges.
Shred-it charges $10 per “box.” A “box” is whatever unit of packaging you bring. Laundry basket? Ten bucks. Banker’s file box? Ten bucks. Shoebox? Ten bucks. Half-full kitchen garbage bag? Ten bucks.
Papa Doug, who is a hard man with a dollar, had to call the poor shlub on the truck some not very nice names to get his 5 half-filled trash bags negotiated from $50 down to $30. Avoid such unpleasantness or prepare for it.