In the end of 2013, the ROI of a GPU was 30-40 days... OMG I miss these days...
I remember that my Radeon HD 7850 1GB was making $8/day while it only cost $200. I really miss those days. Back in the day, you could also mine Ethereum on 2GB video cards.
At least the upside is that the industry is more mature, so there's less risk, but less risk means less reward.