have a look here for some comparisons between providers
http://www.newsgroupservers.net/
- of course the 'free' VM newsgroup service is the cheapest, but groups peered with, completion & retention are pants compared to a paid for service.
To state my bias I use GigaNews on the 25GB per month tariff ($12.99) & either NewzBin (25p per week) or Merlin's Portal (free) for searches.