Swingline SmartCut Personal Trimmer for $4.00.  Order online for in-store pickup at Office Depot to lock in the price and save on shipping.  Otherwise, shipping is $9.95 or free on orders over $49.  If needed, use this Filler Tool to qualify for free shipping.  Here is a screenshot for reference.  It features an alignment grid with inch and metric measurements, trims up to 5 sheets of 20-lb bond paper at a time, and includes an extra blade.