Not so fast. If a transaction costs $100, it will cost $100 to open the channel (and then another $100 to close it).
wrong. why would it cost $100 to open a channel? besides, $100 is a grotesquely inflated number you plucked out of thin air.
If a transaction costs $100 and opening a channel (such as with the Lightning Network) requires a transaction, then it will cost $100 to open a channel in order to spend your bitcoins.
$100 is not a grotesquely inflated number. If the max block size stays at 1 MB, then it could easily go to $100. The transaction fee has gone up by a factor of 10 in the last couple years. It has risen as high as $10 this week and I don't see why it couldn't go up by another factor of 10 in the next couple years.