I would recommend not going super cheap. Also consider what other games have extremely long load times or frequent load screens, as this can provide some benefit to those games as well and doesn't have to be a purchase strictly for PUBG. This is what I got when I first switched to an SSD.

SSD: https://www.amazon.com/SanDisk-Ultra-NAND-250GB-Internal/dp/B071KGRXRH

Enclosure: https://www.amazon.com/Sabrent-Tool-free-Enclosure-Optimized-EC-UASP/dp/B00OJ3UJ2S

I later replaced it with a 1TB SSD, would recommend something like this: https://www.amazon.com/Crucial-BX500-NAND-2-5-Inch-Internal/dp/B07YD579WM

This is the one I use. SanDisk Ultra 3D NAND 250GB, selling for $52.99 right now on Amazon. Paired with the Sabrent Tool-free external hard drive enclosure, selling for $9.99 right now on Amazon.