The 11/23 was one of the lower-priced PDP-11s, based on the F-11 chipset. I'm pretty sure it would have cost a fair bit more than an XT, though, especially fitted out with the necessary memory and peripherals.
That being said, Heathkit offered earlier LSI-11 machines (which used bit-slice processors) for several years. As a student at a high school with an 11/34, I would have loved to have an H11 or H11A at home, but the Apple II+ that we did have served the family well.
A factory-assembled and tested Heathkit H11A, sans memory, storage, or terminal, was $1895 in 1970s money.[1] Buying the kit would save you $700, which would have been well worth it since the CPU board was a stock DEC KD11-HA [2], already assembled and tested anyway.
The 68K had no MMU or even segment registers, so the 68K machines that can run UNIX had, at the very least, some kind of external memory offset adder. I did not know the Apple Lisa had this- it's interesting because Macs didn't have it and could not run UNIX.
The Motorola 68020 has a MMU coprocessor, and the 68030, 68040 have an on-chip MMU. The Macintosh II, SE/30, Quadra, and Centris series were able to run A/UX [1] since 1988. A/UX was a SystemV with X and Finder.
That being said, Heathkit offered earlier LSI-11 machines (which used bit-slice processors) for several years. As a student at a high school with an 11/34, I would have loved to have an H11 or H11A at home, but the Apple II+ that we did have served the family well.
A factory-assembled and tested Heathkit H11A, sans memory, storage, or terminal, was $1895 in 1970s money.[1] Buying the kit would save you $700, which would have been well worth it since the CPU board was a stock DEC KD11-HA [2], already assembled and tested anyway.
[1] https://heathkit.garlanger.com/hardware/systems/H11/ [2] http://gunkies.org/wiki/LSI-11/2