i bought the cheapest i could get $99 before i left on the big tour in January. It worked brilliantly giving short cuts through all the small towns from here to Dubbo on the 900 kms of first day - but then it crapped out & found out nearest store was on the way home again. Spewin because I only really got it to get me through Sydney (spit)
Anyway when i took it back was able to pay a little more (another 80) & get a Uniden. Its the bees knees. If your going above $200 mark, make sure you're able to update the maps every year for a while and if its going to crap out on you it'll do it within a week of using it solid so dont get the extra warranty option - these things are going to be as low as $50 next year so don't go blowing the budget.
apart from all that, never leave it in sight in the car while you're not there, cracking the window & ripping it out of the holder is common fodder for junkies
good luck & have fun