1950's table saw as DIY CNC bed...

[Toolmaker51]

Tough to beat $80 for a decently sized and stable platform. Shipping was probably half of the cost.
If you really want it mobile, there are various kickdown wheel arrangements posted here. Lots like a wheelbarrow, except 2 wheels, and they don't contact until needed.

That reminds me of a certain run of table saws. Ridgid R4511 had granite table and wings 1 3/4 thick. Cast iron is our friend, but granite's a superior sliding surface.
https://www.finewoodworking.com/2009...ablesaw-review