There are fully open projects like Voron or RatRig, and sellers of DIY kits based on them. Potentially a lot of work unless you're interested in 3D printing itself as a hobby rather than as a tool.

Prusa Core One would be a bit more complete OOTB. It is 220mm in the smallest axis (Y) though. Slicer and firmware are open source, but the hardware is not (unlike previous Prusa printers).

Bambu gives you the same capability for much less, but the firmware is not open source (third party open source firmware does exist). I believe the stock firmware also has to "phone home" at least once before it can be used offline.

Even cheaper are less-well known Chinese companies, like Qidi. Firmware is usually a proprietary fork of Klipper or other open source projects; some people have had success flashing the mainline version.