Yeah, AutoMags are very expensive. Plus, you have to load load your own ammo if you expect them to work. Plus, if you buy one of the early ones, it's likely to be full of burrs and sharp edges and won't function worth a damn.
The last TDE I bought was so tight that I couldn't get the bolt back without pushing the muzzle against a workbench. I got it cleaned up and now it's 100%.
The thing with early AutoMags is, they always go up in value, so you won't lose money. Not sure I can say the same for the new ones.