When you say Mac, do you mean MacBook the hardware or macOS the operating system?
I don't think it's possible at the moment to develop for the HoloLens under macOS (the operating system) but it is possible on MacBook/iMac (the hardware) running bootcamped Windows 10. You only need Windows 10 Pro for the emulator, because the emulator requires Hyper-V, which by the way is not so straight-forward to enable on a MacBook. You can use Home edition for on-device development.
From my personal experience emulator is not really essential. You wouldn't really be able to developer well without having seen the actual device . And once you have the device I'd say emulator is obsolete. I used the emulator maybe once and since then happily develop for HoloLens either directly in Unity Editor or on device.
I believe you can find a copy of Windows 10 Pro cheaper than 300 dollars.