i would not even starting now.
wait a couple of weeks and see where the price and difficulty is.
Many factors to consider.
Best deal was for those who already had rigs with old GPus that were payed over already.
New 6 Rx 470 GPU rig would cost at least $1400, but you can sell GPUs later.
6 HD 7950 will cost about $800, but you might get only $400 (or even lower) or so later when you try to sell 7950ies.