Well, the original company was only in production for about 8 months. There were a few thousand pistols made. Problem was, they were selling them for less than it cost to make them.
What's it worth? How much did you pay for it? THAT'S what it is worth!
Seriously so few of these sell, the Blue Book type price guide is useless- you would have to find what a comparable model has sold for. I DID find a couple of the Lee Jurras guns that had sold- these are even more scarce than the AMT guns. One of them,( in 44 AMP, 12 inch barel) went for $5000. There were NINE of those made.
Check the Wikipedia entry for automag, concise history of the companies that made it. I can let you have $100 for it, if you can wait a week for half of that.