To be honest, PBN's are nowhere near as effective as they were a couple of years ago. The chance of getting a manual action against your site is a lot higher.
If you were going to drop a few thousand dollars on buying backlinks, you don't want to have your site de-indexed by Google in 6 months without getting an ROI.
Non-English versions of Google are more linens and are still easy to game for PBN's.
Also, all PBN's are not all created equally. Making sure the domain isn't dropped, different whois details/domain registrars/hosting providers. Also putting relevant links to sites other than what clients have paid for to make this look more legitimate.
Niches with big competition like Pharma/Gambling/Game Hacks/Lead Gen will continue to user PBN's, but bigger SEO's will be diversifying their link building portfolio by building more whitehat links like guest posts and then sending more questionable links like PBN's to them as a tier 2 backlink.