I get about 10 to 15 CDs down to one MP3 CDR. That's from 10 to 15 hours in 700 Megabytes.
Since you want 26+ hours, and using that effort as a guideline I estimate you'll need a MP3 player from 1.2 to 3 gigabytes of storage.
The smallest hard disk based iPod will do fine.
I am interested in purchasing a digital audio device primarily to listen to books. I cannot figure out the storage capacity required to handle an un-abridged novel lasting 26+/- hours. A FM receiver would be nice plus as well. Any size and product suggestions would be greatly appreciated.