I've said it before and I'll say it again...

Call their customer service dept and talk to them. Know what will make you happy and ask them for it.

If it were me, I would explain what happened (don't be a dick about it,) reference the competitors price (make sure they are identical items... same size, wrapper, count per box, etc. and provide a link for them) and ask them if they would replace the original box and honor the difference as a store credit. Be prepared to return the original item if they request it. I wouldn't be shy about asking for the return shipping cost to be added to the store credit. I would also request that they inspect the replacement before sending it out. I have never dealt with Rocky's but they seem to have a pretty good reputation.

But that's me... you do whatever you are comfortable with.