Keep your eye on ebay if GPS shopping... I've been outbid on several items recently!
I love my maps too, but have recently concluded that a GPS will augment my stones hunting nicely. This was proved last week when hunting for this feature:
http://www.megalithic.co.uk/modules.php?op=modload&name=My_eGallery&file=index&do=showpic&pid=6933&orderby=dateD
I could have saved nearly an hour with a GPS, when confronted with footpath changes and deforestation which had changed since the map was printed. This knocked my usually good perception on the head for a while - but I got there in the end.
Cheers
Tim