There were cheaper machines. But generally I would guess all in all it were 2 times the cost of a PC. Symbolics also sold a development environment for Windows

There were cheaper machines. But generally I would guess all in all it were 2 times the cost of a PC. Symbolics also sold a development environment for Windows (called CLOE) and Lisp Machines on boards for Macs and SUNs. TI had a board for Macs too, but TI left the market end 80s very quickly. Symbolics then was also developing a virtual Lisp Machine - an emulator running on 64bit DEC Alpha machines - the software did cost around $5k later. But keep in mind when PCs became viable for Lisp development on a comparable level, it was already end 80s. Something like a Mac IIx from end 88 was not faster and came with a 40MB Disk. I got a used Lisp Machine from 1986 which had a 600MB disk drive - the drive alone was more expensive than 2 Mac IIx machines. When research labs bought machines like such a Lisp Machine in 1982 for 100k$, they were basically ten years ahead of the market. When budget for these projects were shrinking and the competition was catching up (first RISC Unix workstations and then high-end PCs) it was already endgame time. Additionally companies moved some Lisp software away to C++ - because C++ applications were usually thought to use less system resources at application runtime.