If you can handle some interruption to your work then spot instances are probably going to be the biggest immediate change you can make.
Right now a g4dn.xlarge is $0.526/h on demand but only $0.1578/h as a spot instance.
You might also be eligible for a 10k grant from AWS - https://pages.awscloud.com/GLOBAL-other-LN-accelerated-compu...