For the life of me I can't understand the contempt people have for the Zire. I just don't get it. If you just want a basic organizer, it's great, and its hardware limitations won't bother you. The battery is nice for this, too, and something that other Palms are sorely missing at anywhere close to the Zire's price point.
If you just want to use this as an organizer, I'd go with the Zire. The 2MB memory limitation and 16MHz processor won't hinder you fo rthat, and the convenience of the battery should be nice. However, if you want to do more with your PDA than basic PIM-type stuff, you'll have to sacrifice the battery for models with expansion capabilities and more on board memory.
Sony also makes a nice low end PDA in the PEG-SL10, which has a high resolution screen, 8MB of memory, and is lighter than Palm's comparable models... you just lose the Zire's battery, but you do get a Jog dial, which is incredibly useful.
Personally, at the very low end I'd get a Zire *if* you just want organizational stuff. If you want more, skip Palm and pick up a Sony.