Although ferrets can usually find a way to turn anything into a toy, here's a brief collection of inexpensive and safe homemade toys for your curious animals:
Take a pillowcase and fill it with crinkled-up paper, the noisier the better. Ferrets love rolling around on it.
Wash out a clear plastic tub (about the size that holds popcorn or pretzels) and let the ferret hop in and roll around. Cut a couple of holes in the side and bottom for them to poke through.
Tie a large fishing float to a strong length of string and pull it around for them to chase. Or let the float hang by a loop with the string tied to either side of a doorway a couple of feet in the air and watch the ferrets run it across and back.
Cut a couple of holes in a large plastic ball and your animals will be inside and rolling across the room in no time.
Construct a tower out of different-sized boxes taped together. Put holes a various places to allow the ferrets views from different parts of the tower.
Construct a maze out of lengths of PVC pipe and let the ferrets explore.
Take an old cat scratching post, attach a string to the top and dangle a small ball from the string. Now it's a ferret maypole.
Put three or four ping-pong balls inside a small box. Cut holes in the box so the balls are just out of reach.
Make sure that all the toys you use are clean and large enough so they can't be swallowed. Also, be careful how much they get chewed or frayed. When the toys disappear, as they inevitably will behind the sofa or the washer, bring them out and introduce them all over again.