look 3 months back, 5 USD with 1080ti was normal... than it boosts up to 15...
Who is making $15 per day mining with a gtx 1080ti? the thing is barely making $5 and a gtx 1080 is being sold for $1200, using the calculator + total cost will return your investment in 400 days.
My buddy's 30 rig 1080 ti brings in almost 10K a month.
6 brings almost $60 a day on nice hash.