I've thought about mounting a camera somewhere remote for about three months.
 I'd like this camera to take a snapshot once every half hour, without
need for a grid power connection, battery replacement or a change of
film or whatever other recordable media.
 Said rig should be small footprint and visible only on foot, 30 feet
or so away or closer.
 Does such equipment exist?  If so, what is the cost?

Hi there... theres a company call Black Box that handles all sorts of
computer, local area networking, cableing, etc - and they have also
branched over into security technologies, including surveliance
technologies. They also have a reputation for SUPER customer support. 
You can contact them at:
   http://www.blackbox.com
   724-746-5500
They also put out a 250 pg catalog just on Security related products.
Their catalogs are superb, they explain many technical terms, and
provide great diagrams showing how a system can be constructed.
Suggest you give them a try.

You may want to look at devices called trail cameras. These are
cameras designed to be left outdoors and take pictures of game trails,
and have infrared triggers although I think some can be set for timed
shots as well. Some also have a 12 volt option so battery life should
be adequate. I'm not a Google researcher so I won't bother digging
further; perhaps one of them can do so and claim the payment.

I am not sure of  your goal, but  there is a low cost  camera  that
does use 35 mm film, sold in sporting  magazines, or equipment,  with
an  eye  to detect movement and take picture then.  If  you were
looking  at  visitor, or animal going by or what ever, this kind of
elec. eye  camera  might work. I think one mounts on tree or  where
ever, and  set in advance. when all film frames used up, it is done.  
8-10-2005