This is a small cantilevered laser engraver design based on https://www.thingiverse.com/thing:4605853
I used most of the core design, but resized it for 2020 aluminum extrusions and thinned out most of the parts because they don't need the same strength for such a small device. With 300mm extrusions from Zyltech, the working area is about 8"x8". It might be possible to go up to 500mm length but I have not tested it. Any longer and you probably need a wider extrusion for the Y axis.

There is a good discussion about this design over at V1 Engineering
https://forum.v1engineering.com/t/cantilevered-laser-engraver/19179/140

If you search for the best price for steppers and control you can build this for $100-$150.
I use the 7w Neje laser head from AliExpress, Extrusions, Steppers and Arduino control board from Zyltech and it works great.

I have included both .STEP files and Fusion Export files so you can edit and modify for your own needs.

Gantrys need standard V-Wheels (Qty 7), 6mm spacers (Qty 10), 6mm Eccentric adjusters (Qty 3) and M5 bolts (Qty 4 35mm, Qty 3 30mm).
The parts are connected to the extrusions with standard M5 T-Nuts (Qty 12).
The Belt tensioner is attached to the leg using 2 M3 screws but you need brass threaded inserts on the legs themselves. If you want to screw directly into the plastic, just make the holes smaller.

All of the above parts can be found at openbuilds.com or amazon.com. I like the openbuilds low profile bolts, but any will work.