those prices are almost spot on with the hashrates they give…
your going to get 400-450 with a 1070 and 700-750 with a 1080ti.
if you go 1080ti you save on motherboard and CPU as you pretty much build 1 rig instead of 2 for a similar hash
1070 however can mine more coins better than both 1080 and 1080ti. As Cryptohminer pointed out, 1070 is better for ethereum hash/cost of GPU and it is also better for LBRY