Layvin Kurzawa from Monaco is pretty good. He is young but he is more than capable as backup right now and he then becomes pretty impressive in the long run. Plus he is cheap too. They might even be willing to loan him out.
If you really want a new LB, I'd advise looking for a young regen. 16-18 and developing him. You're not going to get a LB of sufficient quality for that amount of money IMO.