If you want to build backlinks on your paid site, I recommend getting links from guest posts, PBNs, press releases, and editorial links.
But if you want to increase links to your PBN, it is not worth spending such high prices for this. Instead, you can get links from Web 2.0, profile links, blog comments, directory listings, social media links, etc. Also, low-cost PBN sites are available for Tier 2 links.