Only one server:
Old: 2.4 GHz Pentium 4, 4 GB RAM, 32-bit FreeBSD 5.3.
New: 3.0 GHz Core whatever, 12 GB RAM, 64-bit FreeBSD 7.1.
PG: "The new server seems to be about 2x as fast. The frontpage renders for me in about 50 msec. But the site should seem more than 2x faster (for logged-in users) because many requests will terminate before being interrupted. There's now enough memory that we can fit all the links and comments in memory at once again. We should be good for another year or so." (traffic: http://ycombinator.com/newsnews.html#15jan09)Not sure of how or where server is hosted or what else is used e.g. router/firewall/bandwidth/ups/utilities/etc., but if pg/rtm billed for time all other costs would be insignificant.
Maintainance:
A lot less than most people considering it's rtm and pg.