Favorite hamster toys for robos?

[Crystalroborovski]

Hi there! In a couple of months, I will be getting a pair of robos (Yes, I've done my research on pairs) and I wanted to ask- to all the experienced hamster owners out there, what hamster toys are your favorites? I am looking for toys that would be suitable for robos, safe for hamsters, suitable for a pair of hamsters, and fairly inexpensive (probably nothing over $20). Keep in mind that I live in the USA, so some hamster toys found in Europe are not available in my country. Thanks!