http://www.superbeetlesonly.com/forum/index.php?showtopic=4008&st=0&p=29570&#entry29570
hopefully the link above will take you to SBO showing how they are installed
Places like Vintage Vee Dub sell them and that are about $500ish for a new set complete.
Late (post 1968) sell 2nd hand for ..... $200 but you will be up for something, pinch welt, a hinge, etc etc.
Expect around $300-350 for a complete 2nd hand set
Also to clarify - your beetle will have the necessary screw holes already there.
As shown in the link it is a relatively simple task to find them.
Cant imaging some one charging more than a $100 or so to put them in "professionally"
[ Edited on 23-11-2005 by Bizarre ]