cheapest site is
http://www.globalpositioningsystems.co.uk
Or at least they used to be when i worked for them.
A hp 2210 is not a bad choice as it has a cf card slot and a sd card slot as well as bluetooth.
Gives you lots of flexability to choose a gps receiver to go with it.
plus its got loads of memory and stuff.
To better it you could use a xda or a xda 2.
All with tom tom software....