42 servers online spread across 3 different network data centers I've come to trust explicitly.
30 of the servers are 1U-2U servers I built myself so I'm only paying for bandwidth on those. The other dozen server hardware is all leased. So 42 servers with about 300mbps per month average bandwidth.
Bottom line: Below $5k/m.
It's good to have friends in the right places.
I myself only use 5 / 42 servers though - the 37 of the other servers I lease out to clients.