Best nail gun?

I am very new to working with tools and am wondering what the best type of nail gun I should buy to work with pallets. I am interested in redoing a wall with pallets that will go right onto the 2x4s that make the frame for the wall. I was going to use screws but decided against that. Don't want to spend a fortune either. Any suggestions would be greatly appreciated. I've attached a picture of the wall before I took the tongue and groove down and a picture of what I am going for. Thanks!
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