New Jersey tax lien question! Noobie

Hey guys I have a simple question on tax liens in New Jersey. I am looking to buy a few cheap liens to get my feet wet and possibly get a good return on a few hundred dollars. Now my question lies is in the cost of sale + the lien cost. When / if the homeowner goes to the township pay their bill / my lien off. Will I get the lien amount + interest + the cost of sale I was charged??

The lien I am looking to buy is around 250$ and the cost of sale is 70$. Will I get interest (hopefully) on the 250$ and I will paid back that 70$ ?

Let me know if this makes sense or if need be worded differently.