Navigation and location?

Is there a low-cost solution to determining the position of a bot in say a large field? I've researched GPS/INS (Inertial Navigation System) and
apparently there is a self-contained chip that does this. There are two down sides. One, it only has 3-meter accuracy and two, it costs $6750 (yuck!).
Sure, it's intended as a military component and is therefore 10-20 times more expensive than it needs to be but you'd think for that kind of money you'd get better than 3 meter accuracy. My Magellan with WAAS can do that well some times.
What I'm looking for is a system that would have an accuracy of a foot or less.
Blair M. Burtan Northern Lights Productions
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.