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$300 in transaction fees is ridiculously too high. I dont care how many inputs are there. Personally I am on pause in BTC transaction, until this mess is sorted.
you can try any other cryptocurrency (the altcoins) but let me save you some time and say all of the altcoins that i have seen so far will require a huge fee amount for a transaction that is as big as
20912 bytes (~21 kB) it may cost less in $ just because the altcoins are cheap but it doesn't change the fact that you pay for the size in byte.
He would have to send his Bitcoin to an exchange - so pay the transaction fee - to be able to buy an alt.
It isn't a solution, unless he finds someone who is willing to swap private keys, which I wouldn't recommend as they might have copies anyway.
Just pay 50 sats now, that will cost you $40-50 for the transaction. It sucks but now is a very good time to do it.