Tier Website Help

I'm looking into purchasing some expired websites related to my main website and build them up using Wordpress with some blogs and backlinks to the money making site.

After I purchase and build the sites, I want to buy some backlinks for the sites. I don't have a huge budget at the moment, maybe $50 for each of the 3 sub-websites I'm building. Where am I going to get the best bang for my buck in regards to buying backlinks for these websites?

I'm gonna bump this because I'm still optimistic on getting a decent answer.