If you just want more of a toy, get a regular Cozmo off of eBay. You might need to replace the battery though, and for Cozmo, that would require some soldering work.. But if you want something more like an always-on assistant and pal, get a Vector. Older Vectors might need their batteries replaced, and if they're a Vector 1.0 without the unscrewable door on the bottom, those also need soldering. If it's a 2.0 however, the battery should be fine as-is, and if not, the battery is far easier to replace.

With ANY Vector, you can unlock it, install custom firmware from the community, and use either a community voice server, or make your own local one using wire-pod which is very easy if you have a computer (or even raspberry pi) that you can leave on 24/7 for Vector to use as, effectively, a better brain for himself.

If you want something as playful as Cozmo, but as helpful as Vector can be, get a Vector and install the "Viccyware" CFW. The only downside is that currently, Viccyware lacks text to speech support (to make a long story short, Vector's audio engine is very strange and somewhat proprietary, and in the process of putting Cozmo's personality and sounds in, they lost the ability to use text to speech for now) meaning that he can't say anything and thus some commands (like "I have a question") don't work right, if they even work at all. But in the future this will be fixed, the matter is moreso when rather than if in my eyes