These are the ones that you just have to really double and triple check that they will wok for what you need them for. Ideally you do not need them to do all that much, which is why you can afford to save a little bit.
A Kindle Fire is cheap enough and works well. I picked up a HUDL Electron for a project as a budget tablet - since I didn't care about the low quality front camera (which I wasn't using for what I wanted) it was fine, just a bit slow to start. It cost under 100.
