The same rules as ‘beds’ apply for toys. Cats are curious and apart from eyesight often go by sound. Anything crackling, rustling or popping will catch their interest and make them inquisitive. A paper bag from IKEA, a rolled up piece of paper, some popping wrap material, a string tied up with some pieces of paper at the end, a carton with some paper inside, some ribbons tied into the washing basket you use as carrier, a ping-pong ball, or the cap of a ball-pen make wonderful inexpensive toys.

If you find toys which require the kitty to think and activate some movement (e.g. the scratch-pads with balls) then by all means go for it and spend the money. But keep in mind: a decent scratch tree is much more important and rewarding then the most fanciest toy with battery.