First, your hardware store is a ripoff. (Mini storages also do this) it’s the cost of convenience. Do you really want to make a separate trip to save $2/box?

For the record small boxes should be around $1 and larger ones for $3-4 depending on if they are triple walled corrugated or regular.

Having new boxes delivered is motivating, saves time, and you can get packing materials too. New boxes are delivered flat with the flaps attached so before you tape the bottom you can fold the flaps down and they’re kept out of your way. Every little bit of effort saved counts when it comes to packing a whole house