ive moved about 18 times in the past 3 years i have found that dumpster diving behind grocery stores os a good way to aquire boxes just stay far away from the ones that read "produce"
Try Kroger's really early in the morning. Or ingles on merchants late at night. They usually have some really big boxes they are more than happy for you to take while they are restocking. You can break them down and then retape them and fit a whole bunch in your car.
“A gem cannot be polished without friction, nor a man perfected without trials.â€
Denny's will also give you free boxes, they have sizes from small to huge. Just call and ask- I suggest calling at like 9 or 10 pm mid-week (Tues, Wed, or Thurs) and asking the manager on duty.