I have ordered a lot of cactus from ColdHardyCactus. I think he is one of the better vendors out there. I hope you called and complained about your dead cactus but as he took a loss to sell it to you, he may not want to hear from you again. I do doubt that he sold you a dead cactus on purpose. The cactus always come bone dry as watering and then closing the plant in a dark box for a week would mean certain death.
I think his plants are reasonably priced already; you paying postage to get them to you is part of your obligation as a buyer. But I never order one plant - the postage is high for one, but you can add 14 more before the postage changes. If you want the plant, you pay the price, in this case, plant plus postage.
I have gotten a couple orders that were wrong and/or incomplete but he has always made good on them. Yes, his computer skills are nonexistent but he is an expert at growing cactus so I am willing to forgive him for his lack of computerease. I have only lost one of his plants - a squirrel ate it.