Oh, you are on the 200 plan. Yeah, that's a bit more of a difference, but where are you getting $60 from? If you are adding the $45 on top of your original $15 you don't need to. It's only $45 a month for 4GB of data AND tethering.

Still a lot, but if you only do it a couple months a year it'll easily save you money. Over the past year I have literally had no need for 3G on my iPad. I'll definitely be firing up the tethering plan once we head out on our next vacation though.