For our original server, after the first full day after the HN post, we racked up an AWS bill of about $1.62. Most of that was in the first few minutes after the announcement before we implemented the user cap.

From earlier today for about 20 hours of run time: we had 13,000 successful connections to the server, 22,000 failed attempts to connect. The server is averaging about 100k per second outbound when fully loaded with 20 clients. With the quick improvements we made after the HN flood we got the CPU down to about 1-5% on a t1.micro when 20 clients are connected and interacting. The real issue for us is the bandwidth.

The server and protocol could be MUCH more efficient (visibility pruning, binary messages, etc). But it was something chouser and I hacked up over the weekend and it's now working quite well within the cap.