The cost of the setup above is high. Especially the memory part, which charges $50 for 500G per month.
Since the LN node eventually doesn't use the btcd Bitcoin node, there is no need for such a large disk. I believe 8G is enough, and also a micro instance with 1G RAM is enough for LN.
Decreasing memory in AWS is a pain. I used MATT BERTHER's 'How to Resize AWS EC2 EBS volumes' for that, but make sure to take the advice in the comments.
The other more troubling aspect is the payment for data traffic. I got charged almost $60 for the last month, with around 800GB download. I suspect that it was mostly new Bitcoin nodes asking for download of the whole blockchain.
To try and limit the possible traffic I added maxuploadtarget=144 to bitcoin.conf and restarted the daemon. This limits the number of full-blockchain downloads in a smart way. I'm hoping this will keep the bills somewhat sain.