If you used a jig, like from DPH Arms.  Would you be able to bend a flat using as vise or do you really need a 12 - 20 ton press?

A vise would work if you prebent it I think.  (anyone know for sure?) I can bend the receiver by hand so I can't imagine it would take a lot to set it into a vise and crank down.

I used a 12 ton press & homemade jig on mine $70 from Harbor Freight isn't bad really.  You probably don't even need a 12 ton, you could go real cheap and get a 6ton.

Where there's a will there's a way I guess.

I've got an ak-builder jig that I love and I smoosh it under a 12 ton press.  I have to really put some pressure on it to get the flat to bend.  I don't think a vise would do it.

On the other hand, I have seen a thread somewhere where somebody bent a flat using a jig and big 'c' clamps.  Also one guy smooshed a jig between a jack and his house (bad idea).

Overall, $100 for a press is a good buy- you can do rivets, barrel pins, barrels- whatever with the press.