I created this list of reliable Usenet providers that offer free trials so you can test their service:
TweakNews Usenet Trail
TweakNews offers a 10-day unlimited free trial. This reliable European provider has it’s own Usenet backbone. Credit card or Paypal required.
Usenet.Farm Usenet Trail
Usenet.Farm is an independent Dutch provider. They offer 20 GB of free downloading. No credit card or other payment is required, only an email address.