To answer your original question: not much. They've claimed that the $31 price I paid was a 'glitch.' They said that while they understood it's frustrating, they won't do anything to remedy the situation besides refund me my $31. They said their refund process takes ten business days. It's been well over that and no refund in sight. But to be honest, I'd much rather get access to the domain I bought than a refund.
Their most recent message to me was asking if I want to proceed with buying the domain at the new $8000 price. Since I guess I have unwittingly been forced into a negotiation even though I used 'Buy Now' and the original funds I paid have already left my bank account, I don't have any faith that Namecheap won't allow the seller to continue to ratchet up the price.