Sorry to hear of your rust problem. Not to rub it in, but I want to reiterate what another has already said.... never store guns in cases... only transport them that way ... assuming it might be safe in your house (no kids etc) you're better off standing the gun in a corner of a closet not in a case than leaving it in a case... air circulation around the gun will resist condensation form settling...A cheap metal gun locker (you can get a 8 gun cheapie with decent locks for under $100.0 if you watch the sales) is a pretty good way to go.
Now that you've got the rust all over the gun you probably are looking at a complete blue-job.
Take it to your most trusted smith and get an opinion and a price.
The good news is that if you have to get it blued you're gonna end up with a pretty new finish to admire and maintain.