Amazon Basics 8-Sheet Capacity,... https://www.amazon.com/dp/B00YFTHJ9C?ref=ppx_pop_mob_ap_share
I use this one and it works for most cardboard. If I were to buy another specifically for composting cardboard I would get one that can handle more sheets. Most cardboard goes through easily but thicker material can get stuck. This helps me get enough brown material and with my current mix it decomposes within a week.
https://www.amazon.com/dp/B00YFTHJ9C/ref=pe_825000_114660910_TE_ite
This is the one I received as a gift. Under $50 and is able to shred cardboard (at least from Amazon packaging)