Usenet servers and services continue to evolve; few providers offer much in the way of 'block' accounts anymore, partially because the reliability/retention of most operations, coupled with low-priced 'unlimited' accounts, mean that the old 'nessesity' of maintaining a secondary server account to 'backfill' parts is mainly unnessesary, unless of course you are counting on ISP provided news-servers, or have some sort of capped account provided, again, with your ISP.
Or, you simply have a poor server; but those mentioned are almost the ONLY block account providers left these days, in particular usenet-news and Astraweb. I still have some Gigs left at an account at Astraweb, left over from before I switched to Giganews, and left the 'attempting to fill' days behind. But most large providers have excellent retention.
The best pricing, in doing a quick look-through, is Usenet-News, as low as 30cents/Gig. There are a few folks using 'Cingular' pricing, i.e., 'roll-over' plans that take your limited Bytes monthly accounts and 'roll-over' the unused bits. But in quickly scanning those deals, the bits DO eventually expire, just like the minutes on Cingular Cellphone plans. So, sounds good up front but watch the fine print.
What's interesting is the number of server plants that seem to be in co-location facilities under the 'Highwinds' company. (i.e., do a tracert to their servers). A large number of them seem to be located in Phoenix, AZ.