So I've been looking into RTK related GPS stuff off and on for months, may start a GPS related area and document my findings, but was looking at this kit, and while it is cheap compared to many others out there it is still well outside my "toy" limit!

So in digging more I came across these from navspark that are RTK capable:

Maybe pair that with an arduino based talk2 from this nice guy in AU (which I own a few of these for another project):

Still would need a decent antenna for the GPS module, but at say $100/device compared to $250 or $500 may be in the ball park for a project for me. Note: I mention $250/each as I'm pretty sure I found another site the other day with a pair for $500, but not finding it right now.