Linux

You could spend your limited time and energy setting up an emulator of the powerPC architecture, or you could buy it at pretty absurd prices — I checked ebay, and it was $2000 for 8 GB of ram…

You're acting as if setting up a ppc64 VM requires insane amounts of effort, when in reality it's really trivial. It took me like a weekend to figure out how to set up a PowerPC QEMU VM and install FreeBSD in it, and I'm not at all an expert when it comes to VMs or QEMU or PowerPC. I still use it to test software for big endian machines:

#!/usr/bin/env sh

if [ "$(id -u)" -ne 0 ]; then
    printf "Must be run as root.\n"
    exit 1
fi

# Note: The "-netdev" parameter forwards the guest's port 22 to port 10022 on the host. 
# This allows you to access the VM by SSHing the host on port 10022.
qemu-system-ppc64 \
    -cpu power9 \
    -smp 8 \
    -m 3G \
    -device e1000,netdev=net0 \
    -netdev user,id=net0,hostfwd=tcp::10022-:22 \
    -nographic \
    -hda /path/to/disk_image.img \
#    -cdrom /path/to/installation_image.iso -boot d

Also you don't usually compile stuff inside VMs (unless there is no other way). You use cross-compilation toolchains which are just as fast as native toolchains, except they spit out machine code for the architecture that you're compiling for. Testing on real hardware is only really necessary if you're like developing a device driver, or the hardware has certain quirks to it that are just not there in VMs.