Before I got a Nexus 5, I was on PagePlus's 250MB and then 500MB plan. It's very doable to stay within those limits if you understand and are okay with cutting back on certain things. My experience was on Android 2.3, so keep that in mind as some things may use more data now.
- Droidwall app -- you can limit the apps that can use data.
- The Dolphin (maybe others?) have the setting to disable images on webpages.
- Once a GPS route is loaded, it should take you to your destination with data disabled. From my experience (not a heavy driver), using GPS with data enabled didn't use a ton of data.
- And...tweaking the rest to your personal preference.
Extreme data saving does inhibit some of the smartphone experience, but I'm sure you would survive either way.
You can always change your mind and switch plans, so it doesn't hurt to experiment a bit.