Tell the neighbor to keep his infected birds in his own yard in no uncertain terms. You may want to consider documenting when his birds show up in your space with photos. I don't know how you feel about your neighbor, but a total flock loss (which could be looming in your future) is not going to be easily rectified. Documented evidence that your neighbor was negligent will go a long way towards recouping your financial losses. The loss of treasured pets can never be recouped, but...
You should consider having your flock tested. If/when they start getting sick you will at least know what you are dealing with. Your county extension agent can help you out with that.
I am sorry your neighbor is an irresponsible jerk. I hope his lack of responsibility has not ended in your heartache.