Nothing to add really, just to endorse Walk Tall's comments about the Oregon 300.

There are many, many more options. I have even seen people using the sat nav out of their car.

Going down the Oregon route is quite an expensive option. The GPS will cost £200+ and if you go for OS maps you an expect to pay a minimum of £100.

As Walk Tall says; go to an event and see what people are using. You will find that most people are more than happy to show you how things work. A useful web site for looking at GPS units (probably the cheapest as well) is http://www.handtec.co.uk/section.php/345/1/outdoor-gps