Here in Germany, Newcastles is the only mandatory vaccine. There is an oral vaccine that has to be administered every couple of months, and it has to be administered via drinking water within 2 hours of mixing. There is also an injection which is good for 1 year: Nobilis Newcavac is what my vet gets. Of course how long it actually provides protection may be longer, these are the intervals that are mandated. If you are doing this voluntarily, you may be able to have a blood test done to see if it is still good.
And yes, the doses are geared towards mass production farms so for about 1000 birds. But here, we can split costs since everyone needs it.