The trade name for the original $6500 cube was the NeXTcube (68030). The names for the pizza box workstations were the NeXTstation (68040/25 MHz) and NeXTstation Turbo (68040/33 MHz). The NeXTstation spec’d out at 15 MIPS.
You could buy a NeXTstation for $4995 on the open market, and considerably less with an educational discount.
You could buy a Sun Sparcstation 1, which was released a bit earlier and ran a RISC 20 MHz processor but it was $9,000.
If I recall correctly, SGI workstations like the SGI Indigo at the time started at somewhere around $7500 and depending on configuration could be nearly $40k. The SGI Indy, which was the low end SGI machine, was faster and priced at an identical $4995 - but it wasn’t released until mid 1993.
The first Macs to use the 68040 weren’t released until mid 1992. And they also cost $7,000+.
I am unaware of a machine that was available in 1990 for under $5,000 that had more horsepower. If you can point me to one I’ll gladly concede. But at the time I was actually a NeXT campus consultant, which meant I was selling them and knew the specs of both the NeXT products and the major competitors, and I’m not aware of one. Certainly by 1992 the Mac and high end PCs were catching up, albeit both with vastly inferior operating systems.
That was a long time ago and I could well be wrong. But if so I want to see evidence.