AmigaOS 3.x is still common by people running emulators, and legacy hardware, and the Vampire V4. AmigaOS 4.x is still under active development for legacy hardware with PPC accellerators and "modern" PPC Amigas.
Then there's the open-source AROS and the commercial MorphOS too.
It's a mess.
So there's new hardware (that's not branded Amiga for legal reasons, but can run AmigaOS), old hardware, and everything in between.
For those who "just" want the cheapest way of running Amiga software, and don't have any particular reason for wanting one of the PPC boxes, an x86 PC with UAE (Amiga emulator) or AROS + UAE is a far cheaper option.
For those who wants something closer to the "classic" hardware, there are a number of FPGA based options with various degrees of advances over the classic hardware.