A 120GB SSD (ideally a little greater.....240GB if you can stretch to it.... usually around $70 or so).
Optane is a cache drive (essentially what an SSD was ~7 years ago). Considering you must be on a x2xx chipset, and a KabyLake CPU to run Optane.... it's a waste IMO.
Even a 'budget' SSD will outperform mechanical storage + cache drive.
If you can stretch to it, this would be a great option:https://pcpartpicker.com/product/vwPzK8/pny-internal-hard-drive-ssd7cs1111240rb