Depends on your country but I was involved in the running of a Minecraft server a couple of years ago with about ~100 simultaneous players and our server costs

Depends on your country but I was involved in the running of a Minecraft server a couple of years ago with about ~100 simultaneous players and our server costs were about £400 ($650?) a month in a UK datacentre; so $1000/month wouldn't be impossible. We could have saved some money by using a cheaper European provider (iirc OVH had a similar spec'd server for £200), but we were all based in the UK so the low latency was a major benefit. The UK server provider market really needs some disruption.