Given that the server is going to be inactive for a fair amount of the time, would it not be easier to organise a host depending on who is currently there, ready and willing to play? So for example if at a certain time there are, say, 5 peple active and waiting to play some mission, one person just drops a line on the sticky topic, or in IRC, and says 'OK, MP server up at blah blah IP, we're playing (or testing) such-and-such a mission, join in the next 10 minutes' or something? Of course, it could be a little more organised than that; there could be designated times in the day so that people know when to look for games.
That way it's not one person shouldering the cost for a long time (as would happen if one person supplied a server on an ongoing basis), the cost is spread amongst everyone because different people play and host at different times. Plus it aves on wasted time when there is only one or two people playing, or no one at all.
Just my thoughts
EDIT
> Mission requires restart
From experience, it is possible to drop a mission into the OFP mission directory whilst the program is running, and then find it and play it, all without restarting the game itself. Of course, the same is absolutely not true of addons, so missions using new addons would indeed require a game restart.