side note: I have contacted Mikal Hart- the original creator of the Reverse Geocache box.however, he does not have the time to tackle this project.
I know all of the above is a bit much to digest...and at first glance- this appears too be very complex...when in fact it's not.
The legal stuff does not seem all that bad really. If the original poster wants one just for his own use I don't see any problem at all.
Personally this is way too much of a project to get involved with, at normal rates I reckon one should charge about $20 just to read the post, unless you find someone with nothing else to do (student, retired etc) who wants the experience and doesn't charge properly you won't get out of this for < $1000s IMO.
If I spent the time to develop one for you, I'd be looking at creating the code and hardware interfacing to be generic enough whereby it would become a commercially viable product which would decrease your development cost assuming I could factor my initial costs across potential future sales.
<cfset fn1 = #val(90-Current.latitude)#><cfset fn2 = val((PI()/180)*#fn1#)><cfset fn3 = #val(90-Destination.latitude)#><cfset fn4 = val((PI()/180)*#fn3#)><cfset fn5 = #val(Current.longitude-Destination.longitude)#><cfset fn6 = val((PI()/180)*#fn5#)><CFIF (fn6 eq 0)><CFSET distance=0><CFELSE><cfset distance= 3963*ACOS(COS(#fn2#)*COS(#fn4#)+SIN(#fn2#)*SIN(#fn4#)*COS(#fn6#))></cfif>