RADISH, I'm no lawyer but you would appear to have an...

RADISH, I'm no lawyer but you would appear to have an enforceable contract there.

Have you contacted ebay?, if the seller is an ebay regular you would have more weight on your side as this type of behaviour by the seller can get them permanently banned by ebay. If it is only a one off seller ebay certainly would do something about it but how effective they would be is the question.

No idea of the small claims court, I always do my very best to steer clear of lawyers, courts, etc as it usually seems that whether you are right or wrong is pretty immaterial, it really only matters how much money you have to spend on the case.
However the ebay records would give you a very strong case that the item was sold to you at the price. Have you read the fine print about the ebay terms and conditions?, should be something there for this type of thing.