rs looks good
http://img-asia.electrocomponents.co...C311269-01.jpg
about $13
http://img-asia.electrocomponents.co...E749935-02.jpg
about $90 for 500mm if i am going to be driving the external circumference of the dob mount
http://img-asia.electrocomponents.co...C440420-01.jpg
cost $77 and a 100:1 gear reducer
http://img-asia.electrocomponents.co...C718852-01.jpg
$168
need to get to 2400:1 , so need 24:1 somewhere else along the way