Those are great tips!

Don't forget boxes, cardboard boxes. You can keep them single, or cut holes in them & atach them. They are great!

Old clothes, especially t shirts, baggy pants etc.. they love to tunnel through them.

Plastic soda bottles etc...

there are so many other cheap or free toys you can have for ferrets

a box filled with UNCOOKED LONG GRAIN rice NOT minute rice or anything though.
Or filled with clean sand, plastic easter eggs etc..

I could go on & on but I am lilited for time tonight!