I've heard that pawn shops are a good place to buy a cheap GPS. For all of the reasons you can think of, they're fairly plentiful there. Sounds to me from what people have recommended, look for a later model Garmin.
I've got an older Garmin, no free upgrades, so being the cheapskate I am, a lot of the places I go aren't mapped. Like when I use the bypass around Waldorf, it tries to turn me at every road to get to 301- and where I work doesn't exist. I'm "okay" with the Garmin, but I do have an issue with how all types of GPS I've tried (garmin, tomtom and yzphone thingie) map the trip. Even though I have it set up for "quickest route", it tries to take me via the first turn available, even if it's not the quickest routes. If I miss a turn, rather than u-turn me, it'll remap using my current location as the new start of trip (which based on the first turn route I just mentioned can turn it into a completely different trip).
I don't have a smartphone because our cell coverage is so bad at home it would be pretty worthless, but I've always wondered what would happen if I was using the smartphone GPS and my kid called and wanted to talk. Would I have to pull over and take the very important call or hang up and get to my destination and call my kid back?