Giganews is comparatively expensive. Usenetprovider, Easynews, and dozens of other providers offer similar services for much, much cheaper.
Giganews does have amazing retention, however. I think they're up to four or five *years* for text-only groups. And they have SSL, which most others don't.
Your best bet may be to purchase a chunk of transfer with no expiration date. I have the unlimited DSL plan from AstraNews (~70 day retention for binaries, much higher for text groups, maxes out my connection at 750k/s), but they also offer 25gigs for $10. And for a text-only user, it'd take you forever and ever to use up 25 gigs.
Providers used to offer text-only plans, which worked out to just a few bucks a year, but I guess Google News killed that off. I checked some of the bigger providers for you and couldn't find anything.