I have two Discourse instances:
- One quiet forum on 1GB VPS: http://cd-rw.org
- One busy forum currently on 2GB VPS: http://tappara.co
They both run fine. You can potentially stretch the capabilities of a 1GB VPS by using zram, which I have done - so far so good.
With 1GB VPS slice costing 10$/month, is it really worth the effort try to push Discourse down to 512mb? I mean, what would be the expected savings - 60$ a year? If you have some actual traffic on your community, just add AdSense to help with the financials.