Thin, light, but mid/low-range?

Hello all. So I have to get two new laptops for work. I run a research project and the computing needs are a bit all over the place. My main laptop is a Sony Vaio, we will be getting a Macbook Pro soon, but now I need to get two cheap laptops and would like your advice. My requirements are modest. I do not need discrete graphics, a HD display, a huge hard drive, or an external drive. 4 GB RAM would be enough, and the screen can be less than 13." Ideally, each computer would cost under $500. It will be used in the field, so a combination of lightweight and durable would be good. Any recommendations? I have thought about Chromebooks but not sure we can be that cloud dependent. Any other ideas?