To be honest, your budget is too low for a decent quality ready to run machine in that size.
Anything in that size and price range, will be a low quality light hobby grade machine.
Zenbot's are made mostly of plastic.
You might be able to find a chinese import, which are usually mechanically much better, but often have subpar electronics.
A Camaster Stinger is a good machine, but starts at more than double your budget.
Stinger I | Small CNC Router | CAMaster
Here's another in the same price range.
https://www.axiomprecision.com/pro-plus-series.html