If you really want to start using your iPhone as a money saving gizmo, getting a solid GPS app is the way to go. Sure, they tend to cost more (a lot more) than your average app, but think about the alternative. There are plenty of people out there driving around like loons, taking directions from Sean Connery voice coming from a $150 box sitting on the dash. Come on people, use your iPhone's.
But don't get stuck using the Maps app that's included in your phone. It doesn't have any cool view options, seems to only find Circle K's and 7-Eleven's when you search for "gas station, and won't talk to you when you need a friend the most (when you're lost). Only the love of a good GPS app will stick with you through thick and thin. Well, unless your battery runs out... make sure you get a car charger.
MotionX GPS Drive
The original mother of all cheap GPS apps, MotionX GPS Drive only costs 99 cents. Less than one dollar! Included in the app has live GPS Navigation, all sorts of options to change your route preferences, and best of all, an amazingly well organized search function. Instead of leaving your fate to a Google search on your area, MotionX finds anything you want around you, from airports, to restaurants, to grocery stores, to hospitals.
Voice settings are optional on the app, and unfortunately it does cost money. You can either purchase voice for $2.99 a month or $24.99 a year, depending on what you want. I know what you're thinking, "hey, that's not so cheap!", but it's still cheaper than most of the rest. The cheaper price may be due to the fact that there is no option to have Sean Connery guide you around town, but such is life.
Mapquest 4 Mobile
So when I said that Motion X was the original mother of all cheap GPS apps, Mapquest 4 Mobile took the crown by being free. Free voice, free navigation, free everything. It's definitely the cheapest of the bunch. It's a bit slow, though, and the search features really aren't that great. If you are looking for a big chain of something or another, like Sonic or McDonalds, you are in luck, but anything that is local is in the dark. I did a search for Liberty Market in Gilbert, AZ, a popular restaurant spot, and the app came up with nothing.
It's hard to beat free though. If you know where you are going, and you have an address if the place isn't a chain, this is the app to get.
NAVIGON Mobile Navigator
I always hear NAVIGON in people's lists of favorite GPS apps, and it's no wonder why. It's clean, it works without a data connection, and it offers more features than your average bear. It offers text-to-speech street names, Reality View, which shows you what lane you should be in to get off at the correct exit, real time traffic ($19.99 lifetime fee), live weather updates, and "Clever Parking" which shows you all of your parking options by your destination. At no point in using this app will you long for your standalone GPS box, and that my friends is a huge plus.
The app does take up quite a bit of real estate on your phone (1.52GB for the N. America version), but having the ability to use the app in the middle of the desert is well worth the plot. If you want to lower the land grab (and lessen the cost a bit, too), you can buy regional versions for only $29, making NAVIGON one of the less expensive options on the market.
My favorite GPS app of them all however is CoPilot Live. It's fairly affordable at only $19.99 ($4.99 if you only want the USA), and gives you the same premium feel that NAVIGON gives you. It has text to speech street names, Live Traffic (for an extra $9.99) that automatically re-routes you around traffic messes, and a live services package ($20/yr.) that gives you live updates on various gas station prices, among other things. It also has really big buttons, which come in handy when you're fumbling around with your phone while driving (which you're not supposed to do). Best of all is that CoPilot is fast. Faster than all the rest, and speed makes me happy.
In case you were wondering, CoPilot, like NAVIGON, downloads the entire app to your phone allowing for offline navigation. Also like NAVIGON, the file is huge. 1.33 GB huge to be exact.