You can get some awesome deals in the States by watching the sales. One caveat...many of the GPS touch screens made by Sharp develop faults when left on dashboards in the sun. Symptoms include freezing or locking up. This affects many of the 3.75" to 4.25" automotive GPS displays, regardless of manufacturer. And buying in the states complicates the whole warranty issue, usually leading to extra costs for shipping, etc.
You can buy a nice cheap turn by turn voice GPS in Canada for under $200. Some nice Nuvi's go on sale at Fry's for $99US occasionally. Keep it out of the sun and you should have no probs.
My GPS is an Asus Netbook with XP Home and a 10" screen running MS Streets and Trips 2009. The USB antenna is a USB Dongle and the whole thing came in under 600 with tax. Also good for when I travel, I use the computer with my Magicjack to make free phone calls to home from anywhere in the world.