I'm no ebay guru but I do recall ebay's legal notice that states bidders are entering into a legal and binding contract . However, you always hear ebay stories of people bidding on stupid things (heard about the $200k cornflake?) and these "contracts" not holding up.
I see you are in CA and car is in NE so it's not exactly easy to walk down there and get the car. Have an attorney right a letter saying they have 48hr to comply and if they don't you still have your options. They are only out $2k since its below invoice and they could be hit with $2k in legal fees pretty quick so I don't see the incentive for them to go the legal way.
One thing is if they sell the car to some else (ignoring you) it could get very messy legally if you win (ie selling the car twice). You have the upper hand, and I think they will honor the deal eventually but you might need to twist their arm a little. Good luck...
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