I'm planning to sell my Felicity scenes & settings. Since it's large I'm planning to cover it in bubble wrap. Where do I find a box to fit this size item? I usually mail smaller packages and just go down to a mom & pop type pharmacy/post office. I would prefer to get a box to bring home and then leisurely put it all together. I was planning to get it all together and then take it to the mom & pop to send. Would UPS be better than a major post office? Is there some other venue where you all buy large-item boxes?

In addition, I hate having to pay for boxes so the cheapest route would be my preference.