Good ol' asda:
if we get over 15 members we could easily rent out a passworded server for just £31 a month, if you split that between 2 its just £2 a month, or $4. It would support 18 players.
It would be a UK server though for a few reasons, on average broadband in the america is twice as fast as Uk broadband, so its unlikely American players would lag anywere near as much as a British player on an american server.