Low Cost Setup for Mining - March 2018 - GPU

Well you want to get the best cards to make ROI with what coin(s) you choose to mine.
Now, typically AMD run hotter and are stronger at Ethash, so personally I opt for NVIDIA. I believe the 1070(maybe 1070ti) is the most hash/$ at the moment. So if you can pick those up at a reasonable price like 600 or under then you're in a good start.
Electricity for me is a around .12 per kWh so with 80% power setting on GPUs and OC I do more than fine on covering electric costs.
tl;dr know what you want to mine and go from there. avoid impulse buying on overpriced GPUs.