There's no built-in GPS nor Bluetooth to connect to a BT GPS unit so...
If your idea of a sat nav is Google Maps, you would have to rely on the Skyhook triangulation, which would not work very well unless you only need to 'navigate' in a very densely populated area. Besides there are no voice directions (and no built in speaker on the iPod).
Just buy a dedicated TomTom or Garmin. I can find new units for around $100. Most have 4.3" screens which is considerably bigger than the iPod's 3.5" screen and does make a difference in navigation.
Sure you could buy the $129 TomTom kit but you would have to buy the maps separately, so when you can buy a whole unit with a bigger screen (with the maps included!) for $30 less... why bother?
If you insist on using an iPod, buy a cheap 2G unit off Craigslist or eBay, jailbreak it, buy+install roqybt from Cydia, buy a compatible Bluetooth GPS device (there's a list on compatible devices on the roqybt site), and buy+install the maps on the device itself (TomTom/Navigon/etc). No need for a MiFi. But this set up would cost more than $99 for sure (iPod+BT GPS unit+roqyBT+maps).
The separate Garmin/TomTom unit would be the cheapest and your best bet. And it won't drain your iPod's battery (unless you buy a car charger...).
Hope this helps?