I use a MIO P550 and it works fine (although I'm new to caching and so don't really qualify for an experienced opinion).
It's on the high-end of your price point, but if you're going to use it for road gps as well as normal PDA stuff (Word, Excel, Calendar, Email, eBook, multimedia etc), it's fine.
Had a few bumps learning how to optimize it last year, but it's fine now. I'm agreed though - it's a good PDA but it's not ruggedized like a good purpose-built GPS.
It's got a better battery life than you're saying, but if you turn it's WiFi on, you won't last long. Once again, a purpose-built GPS will kick it around in that arena.
c.