As an alternative to traditional handheld GPS systems and if you have a laptop handy, you may want to take a look at Sony's ETAK GPS (approx £200) - it plugs directly into the PCMCIA slot, and when used with the right nav software (jepp's outstanding FliteMap application for example), you get a real viable GPS / moving map alternative - with a load more functions besides.
I've used this setup a number of times, the only real problem being screen glare on the laptop, and finding a space to put it !
