How hard and how much money is needed to add Nav to my current display?

 

welcome to clublexus. you mean porting over a factory oem navigation system to a non-nav 3gs? that's going to cost way too much money it won't make sense

might as well go aftermarket imho

and fyi, gs350 came out starting 07

 

i used the garmin unit before.. you have to put it on windshield or find a suitable place but, very easy to use and accurate..

this is "suspension" sub forum btw..