I buy a Garmin every few years at Costco, where price ranges from $150 to $350. It comes with a mount etc and I never hide it. I don't think it has much worth to thieves since they are obsolete not too much later. I also don't frequent dodgy areas (to my knowledge). I do use the PIN protection so even if someone stole it the device wouldn't be useful as is, and they wouldn't be able to get my home address out of it.

Every time I ride with someone who has in car GPS they moan about the user interface and often don't use it anyway due to stale map and POI data.