It all depends on what you really need.
Some of my friends that went from small, cheap Sharp 1024K organizers (used mainly for the phonebook features) to expensive iPAQs told me that they would go back to their Sharp's in a heartbeat if they had to pay for the iPAQs themselves (our company provides iPAQs to some of our employees).
Find out what your needs really are and then, find a good deal on the devices. Who knows? Maybe you don't need an iPAQ. Maybe you need two devices, or even more.
I'm using a paper implementation of GTD in a 3-ring binder along with my Creative Muvo Micro 1GB MP3 player on which I carry important files (besides music). Works great for me!