Not all dry cleaners understand the process of cleaning down. If they use perc they will strip the oils and such from the down effectively ruining it. Before I took it to a dry cleaner I would want to know what process they use for down. Personally I would go to the laundromat and use one of the commercial sized front loaders. Just be careful. Some laundromats do not allow down items in their washers because if the item bursts the down can cause very costly clogs to the plumbing. Make sure it is in good shape. Use a gentle cycle and a good down cleaner like the nikwax. Don't try it in a home washer. They ain't big enuf.
When you dry it throw in a few clean tennis balls and use a very low heat setting. It will take a long time to dry but you want to do it right.