You need three things:

1. a usenet client for downloading files. I use SABnzbd

2. A usenet provider. This is where you are downloading from. I haven’t done a huge amount of research here, just grabbed something cheap for now, and I’ll explore more later if necessary: Frugal Usenet

3. and finally; A usenet Indexer. Equivalent to a torrent indexer like TPB, but for .nzb’s and pretty much always paid access. I went with NZBGeek mainly because it was recommended alongside frugal and I didn’t feel like digging more at the time.

At $6/mo for those two, I’d say give it a try and explore more/other options as needed.