For something "future-proof" you have to run fiber. Rural fiber would cost $5 - $10/ft. That's $26k - $52k per mile.
Most rural roads around here have 2 - 3 houses per mile. I'm sure the more rural you go, the less you have.
That's one hell of an install cost per home passed.
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Unless I missed something, back-of-a-napkin calculations say:
on the low side:
$26000 / 2.5 = $10400
$50/month charge to the rural customer gives $125
$10400 / $125 = 84 months or 7 years.
On the high side: 14 years.
scott