I bought a gtx1070 graphics card driver worth about 400$. I have been mining ethereum with it for about 2 weeks now, mining ONLY when I am away or asleep +/-10 hours per day. After 2 weeks or 200 hours of mining I have earned 0.2eth. (Excl. Power Costs) If you are planning on investing in ethereum-miners specifically you need to WATCH OUT as I believe it will be moving from a Proof of Work to a Proof of Stake on 1Nov this year therefore making the miner useless. Of course, you could then switch to another mineable coin but those might not be worth it for small miners.