I was able to solve this based on an answer from Ask Different.
In short, closing Safari, then running the commands below, worked.
sudo killall nsurlstoraged
rm -f ~/Library/Cookies/HSTS.plist
launchctl start /System/Library/LaunchAgents/com.apple.nsurlstoraged.plist
Restarting Safari after running that and trying to go to http://localhost:3000 solved the problem and did not redirect to to https.
Hopefully this helps someone fix this problem.