Looking for cheap parts to build this and play around with

Hi all, I wanted to experiment with a mechanical design that's similar to 3D printing, but doesn't actually print. I'd like to build an XY positioning gantry for 3 relatively heavy sensors. If you imagine a cube, I'd like to have an XY system on the top, left, and right, with a podium that doesn't move and isn't heated, but has a turntable. What are the relatively cheapest parts I could get to build the mechanical aspect of this and experiment with the idea? This is adjacent enough to 3D printing that I hope someone can suggest inexpensive parts. I don't need massive precision (down to 1mm precision is fine enough) and I don't need a large volume (20x20x20 cm is fine, a little smaller or a little bigger is fine too), but it would be nice not to have to recalibrate things at every start, and I would like the thing to be somewhat stiff (each XY setup should hold 0.2 kg easily). I would be doing the digital control myself so I don't need that, and it's not 3D printing so no need for a hot end etc.

I'll need:

- frame (but I can buy standard alu extrusion frames to build the cubical outer frame)

- rails

- positioning hardware

- motors

- motor drivers

- any relevant brackets

- position sensors / encoders

- a cheap motorized turntable

What are some inexpensive, readily available parts that I could buy? Are there any stores that I could browse for inspiration? I'm located in the EU, so stores here are fine, but I'm also happy to buy from China, since that usually ends up being much cheaper, and I'm not in a rush.

Currently I'm looking for the cheapest things I could buy or one step up from that, just to play around with, with full intention that at some point I'll probably scrap the project and buy more suitable parts to build a version 2.

Thanks!