There are so many to choose from, I'd search around a bit on your own to find one that meets your needs. As much as I hate diverting traffic to the place that should not be named, r/usenet has an extensive wiki of providers and is a good place to start.
If you don't care about any of that and just want a single answer, I use Newsgroup Ninja. It's one of the cheapest options even when it's not on sale. But wait a couple weeks, they usually have a significant Black Friday sale.