I'm with Charlee here. I have looked at the photos and wouldn't pay more than fifteen quid. Allowing for currency conversion and the fact that machines are cheaper here, we have pitched in at about the same level. Shame it has a motor on it, but I would say that wouldn't I!
Miriam is right when she says that the case alone could cost more. If you want to make money from an indifferent machine then you massacre it and sell off parts separately. But it's a shame to do that if it sews well and someone would be glad of it.
This machine has that beaten up look, often the mark of a good little work horse. 99s make an excellent stitch. Why don't you keep it? Has it got attachments? If so put on the seam guide and try it out for piecing. If it has the underbraider have a go with that... You could have hours of fun with this machine and end up seriously attached to it. It is worth more for what you can do with it than the money you could raise from it.