I have a Magellan explorist 300, its very good, has the built in compass that the lads are on about the doesnt get confused(note to bring a standard compass in case of problems with GPS)
I use the irish OS maps and just input the point, it seems reasonably accurate in getting u to a tomb but like they say for rock art etc not great. I used the 10 digit GPS reading to get me to Boleycarrigan stone circle and it took me with about 5m which is pretty good.
It durable and tough and i reckon you would get one new in and around the €150 euro mark.