If your focus is on hashrate ASICs should be the best option over GPUs, you can had to Amazon and compare prices there. <$1500 will be a huge steal and to be profitable you'll need at least 6 or 7 of them.

With no electricity cost the potential profit margin is positive if you can manage the rig properly.

Any reason why you're prioritizing higher hashrate over efficiency? You need the machines to work long enough for you to break even and profit.