Arduino.cc server "reseller" is Site5, but the site itself is hosted by "ThePlanet Internet Services". Clients of "The Planet" also include "Hostgator".
We lease a dedicated server from Hostgator, and they lease the server off "ThePlanet".
"ThePlanet" give Hostgator and Site5 bulk rates for servers, so its cheaper using one or the other, rather than using "ThePlanet" direct.
Whatever deal your on at Site5, you'll get a better price from Hostgator for "the same server" but better service. Hostgator have 3 or 4 times the volume of clients than Site5, so their prices are more competitive.
You guys might also look at updating the forum software from Yabb, which uses flat files and has endless vulnerabilities, to something a bit more "this century" like SMF that has a php/mySql backend.