If you are lucky, I've seen in several Target stores small plastic containers that could easily be used for bento, and even better they are in the $1 racks! (Ok so some of it might be $2.50)
However, the $1 racks vary from store to store. The one in the Palisades Mall in Rockland NY had awesome sandwich boxes with 3 compartments, 1 for the sandwich and 2 for smaller things. The two halves snapped together. There were small cyndrilical containers for cereal that have an attached folding spoon. They had a salad bowl with a special top. You fill a hole in the top with salad dressing, and when you press a button, the compartment pops open and the dressing goes on the salad.
They also had small spoon and fork sets, and lots of cute silicone stuff for baking!