Staples offers its Staples Letter-Size Hot Laminating Pouches 50-Pack, model no. 17467, for $9.99. Plus, Staples Rewards members receive free shipping. (Not a member? It's free to sign up.) That's $19 off and the lowest price we could find. These 3mm pouches fit documents up to 8.5x11". Deal ends April 18.
Of note, Amazon offers a similar set in a 100-pack for $8.96 with free shipping for Prime members.