No, it is free of charge 
For my part, I followed, I believe, the same links that you have indicated here in Discourse: 1 and/or 2.
I had problems with latest UserLand version, but not with Termux, thanks to @mkitti’s advice.
In case it helps, these are the notes I took back then
pkg install proot
pkg install debian
proot-distro login debian
apt-get update
apt-get upgrade
apt-get install wget
apt-get install build-essential
wget https://julialang-s3.julialang.org/bin/linux/aarch64/1.9/julia-1.9.0-beta2-linux-aarch64.tar.gz
tar -xvfa julia-1.9.0-beta2-linux-aarch64.tar.gz
rm julia-1.9.0-beta2-linux-aarch64.tar.gz
julia-1.9.0beta2/bin/julia
# next time Termux is run, up arrow key will bring previous commands:
proot-distro login debian
julia