I will second what requiem says. I use DynDns and had to do the same thing to make Web MediaPortal work. I know the basic cost with them is 20 for a simple domain address like tvserver.dyndns-home.com.
I get very good results using aMPdroid to access MPExtended/WifiRemote via a PPTP VPN (using Microsoft RRAS as the VPN concentrator). There is obviously a performance penalty associated with the tunnel, but the Android PPTP implementation is quite good, and the solution avoids exposing MPExtended/WifiRemote to the outside world. That's a big win from a security perspective.