My
Mio Digiwalker C310x does road navigation and also coordinates search. It also tells you where you are by coordinates.
I guess it depends on how accurate you want to be. If within a few metres is ok with you then the Mio would work fine. To get cm accuracy you'd pay big bucks. It's under $150 now and fits in your pocket or the holder that sticks to the windshield when you're driving. Another plus is that it runs Windows CE so you can hack it and do various things like watch movies, keep appointment books, etc...
I've had it for almost a couple of years and I like the screen better than any of the others out there still. I've used it East coast and West coast and in between and never had any connectivity problems. Often it'll even sych up with sats when I'm in the house. It kicks the Magellan unit that we have at work that cost 3x as much in the rear.