I'm strongly considering building a 2 GPU RX 480 rig for $663. Here's the rig on PCP: http://pcpartpicker.com/list/nw7h3F

If my calculations are correct it will pay for itself in 183 days, excluding electricity cost.

Does the hardware look OK? That motherboard is kindof iffy but it seems to work for a few other people.

I haven't looked into powered risers yet though, which I know I will need to.

Whoops, didn't even think that this might not be the place to discuss altcoin mining. I don't really want to burn my 1060 mining ethereum, I use this PC for college and gaming, but if it's viable to mine overnight then I'll look into it.

I'm still interested in cheap used GPUs though.

Edit: another question, should I mine ethereum or ethereum classic?

I'm new to serious mining (I've tinkered with GPU mining on my GTX 1060 just for fun but I know it's not profitable) and I'm considering building a cheap rig with used GPUs. I have absolutely no clue what I should buy; should I buy a more expensive recent GPU or an older GPU that is really cheap, or somewhere in between? Are there specific models you look for when building your used rigs? What should I buy as a newb to serious mining?

I'm interested in mining ethereum or vertcoin since I've read they are profitable on GPUs. I don't want to spend too much on this but the rig needs to pay for itself within a year. Electricity here is about 10c per kwh (USD)

Another thing I'm concerned with is heat. It seems to be one of the factors that isn't mentioned too much. If the rig is putting out a ton of heat, it will raise the electricity usage from the AC. Where do you put your rigs to avoid this?

Thanks