The Liberator was a stamped out single shot solution for occupied countries in WW2.  They were a single shot, smooth bore weapon that used a .45 automatic pistol bullet.  They came with comic book instructions (to breach the language barrier), 10 rounds with no headstamps (after all, we didn't want the Germans to think we didn't approve of their shenanigans) and a stick to poke out the empty shell.  They were a gun to get a gun, and at short range they were more than deadly.  They would keyhole at seven yards, but that doesn't matter with a slug as big as a .45.  They did their job, although not very many were actually dropped to the resistance in question, and most ended up at the bottom of the ocean after the war.  

These guns do make great collector items, but the rarity of the real article keeps the prices high.  But these days you do have more options.

If you want a real one, they go on auction sites like Gunbroker.com for between $2500 and $3500 in various degrees of condition.

Original Liberator

If you want a reproduction gun, and they are being made by  Vintage Ordnance Company, LLC, you can get them for about 650 bucks.

Reproduction Liberator

And if you just want something that looks like one, cast in resin but pretty faithful in details and weight, you can get one from IMA (International Military Antiques) for only $59.  You too can own a Liberator.

Resin Liberator from IMA

And lastly, Vintage Ordnance had three cutaway Liberator study models they had made when they were developing their reproduction Liberator, and these sold off so fast they made more.  You can get these cutaway guns showing the inner workings for only $500 on Gunbroker. (when available)

Cutaway Liberator from Vintage Ordnance