GPU options for dicking about with deep learning

[ZoyzaSorris]

I'm just starting to have gentle mess with deep learning with Python using Keras as I'm hoping to gradually use a bit more of that stuff in my work. Sadly I am now realising I ideally need an NVIDIA GPU (my current one is AMD) to have anything approaching useful processing power on this and this is just about the worst time to try and buy any GPU whatsoever (including second-hand). Any recommendations on best course of action here? Only really want to spend £200-300 max at the mo ideally so I don't know what my chances are of securing anything worthwhile. Used is totally acceptable (or will most of these have been hammered to within an inch of their lives for crypto mining?).