I am a big PDA fan and have been fortunate enough to use quite a number of them.
As it stands, wifi is not practical on a PDA as yet. Main reason being batterly life. It totally and utterly kills the battery. I'm talking 4 hours or less.
That sucks.
Until their is a quantum leap in battery technology, a pda with wifi is simply there for gimmick purposes. 95% of the time you will have it off. Turn it on to make a quick "free" email or web search and then hurriedly turn it back off again.
The better option for connectivity as it stands right now, would be GPRS. At $100.00 a month, it is not the cheapest option but it won't wtfpwn your battery.
As far as convergence goes, the P910 has the best of both worlds.
Solid PDA functionality and solid phone features all with incredible battery life.
It ain't cheap. US$500 - 800
For all the features you requested, the HP (was compaq) Ipaq 5450 has it all and the kitchen sink. Again, US$500 - 800 and the battery won't go past 4 hours with all features on.
In the PDA market you won't get "cheap and feature rich" at the moment. Maybe in a years time.