I also like Erin's Hamsters 10 toys to make from toilet rolls
(linked below). How much substrate do you have for them because one of the best things you can give them is as much depth of substrate as you can so they can dig tunnels. It doesn't work out more expensive as most of it stays dry and you just need to spot clean mostly. Have also added Erin's cage cleaning tips video that really helped me with a cage cleaning routine and means you will save on substrate too and avoid stressing the hammies
https://www.youtube.com/watch?v=NuPeyD6w-CI
https://www.youtube.com/results?sear...+cleaning+tips
Our hamster isn't really that into most toys and just likes hidey places and food lol. But he's a Syrian and I think Robos are a bit more inquisitive and active. But anything they can hide in or run through is good, that is made of wood, ceramic or cardboard. Also you could try scattering half of their daily food around the cage so they can forage for it. Ours gets quite excited about finding bits of food in the substrate and it makes him explore his cage as well.