Amazon offers the 3M Scotch Heavy-Duty Packaging Tape Dispenser 6-Pack, model no. 142-6, for $9.99. Add it to your cart via Subscribe & Save to cut it to $8.49 and bag free shipping. That's the lowest price we could find for this quantity by $5, outside of the mention below. Each roll contains 800" of tape.
Be sure to cancel Subscribe & Save after your order ships to avoid being billed for subsequent shipments.
A close price: Staples charges $9.99 with free shipping for Staples Rewards members. (Not a member? It's free to join.)