That is extremely rusty! I recently was watching a YouTube video about restoring rusty cast iron. There was a lengthy discussion in the comments section concerning different methods of removing rust including how to effectively use electrolysis. It is incredible to think there is a sewing machine underneath all that rust, but based on the videos I've seen online, I know it is possible to clean it up. I removed rust from cast iron before by soaking it in vinegar and afterwards I neutralized the acid with baking soda. I also removed some rust on my bicycle by using a crumpled ball of aluminium foil. And I have heard of restoring rusty car parts using molasses. Good luck with this. I hope you'll come back and post before and after photos.