Sinusbot is pretty good on RAM (with scripts running also!) I run a licensed version with 2 public bots constantly playing music, 1 bot handling administration things (notifying, kicking of users, etc), and 2 personal bots which all 5 of these bots running at the same time have never reached above 800mb of usage.
Now with that being said, this is on a single core VPS running Debian 8 with 1GB of ram. Some side notes is that is also runs a MySQL server and a backup teamspeak server, so my ram usage might differ from the average.