I just bought a 1980's era Juki off Craig's List along with 91 cones of thread for $25.
For the $$ I have invested I think I got a great deal. I have some small crafty items in mind for it and I have a large curtain project in mind. Having never owed a serger before this, yes it did take me 2-1/2 hours to thread it the first time but now I "get it". There are great videos online that helped me learn (and understand the 'why') of threading a serger.
The manual came with it so that was a help. I've run off samples of thread tensions as was suggested on one of the videos I saw.
For $25 I'm having fun in a new sewing field that I've never experienced before. Would I pay mega dollars for a new one? No.