AMT Back up

Have you tried Gunbroker.com? Used is all you're likely to find since that model hasn't been manufactured since sometime in the 1980s. I used to have one, but really didn't care for it much. And there are much better such pistols available today.

There are three Back-Up .45s on GunBroker today (11/22/15), but the cheapest one is $360 plus $20 to ship. It comes with a spare mag and a holster.

I don't know gun prices at all nowadays, but $250 doesn't seem to buy much anymore. That probably depends where you live, though.

Those look interesting, but last one I have seen was $300. We see ones in .380 most often. The .45ACP will probably bring about $350.

Tucson Bill

Doubt if you will find any in the price range that you listed. Supposedly a company called High Standard Firearms is coming out with a new AMT Back-Up sometime next year. Have no idea as to initial pricing or build quality of the new guns but might be something worth checking out if you can't find anything on the used gun market.

There's one at a shop near me w/ box but would have to be shipped (not sure they do) but I can find out for ya. I do not recall the price but seemed to be in nice condition.