you are in the right. You both agreed on price and date for pickup. Just because he could not meet the date does not mean he can up the price. if that was the case every store would change the prices daily as fish grew.
Both agrreing on the price and date put you in a verbal contract. The other guy changing the price is a breach in contract. Unfortunaly not to much you could do. You could take him to court and could easly win but the cost would not make it worth it. Though most states have strict punishment for breaching contracts even verbal ones.
sad to say but if the othr guy not going to keep his end of the bargun, its best to walk away. I would. I would not want to even deal with him after he did that, not only i wouldnt want to deal with him i also warn others on how he does bussiness, which what he doing is not good practice.