Voyager brake booster problem

I have a 1993 Plymouth voyager that still runs quite well and have just put a few dollars into. That said, the brake booster went on the vehicle and my mechanic tells me that a new one cost about $1500 which he knows iam not spending and a used one goes for about $350. He and I have both tried almost every junkyard this side of the Mississippi River and they have all told us the same thing. And that is that you cannot find that part/unit(the entire brake booster unit) for that car since it is too old and they are not around anymore. My mechanic even tried converting the car to where it would not need it but he said that there was not enough space to do so. Are there any solutions to this or do I have to bite the bullet and junk the car.

Thanks B1, ill have a look at it.