The cost would run in the millions ...
Possibly*... The high end of the range may stretch into the millions. It's tough to say. The name is worth exactly what the highest bidder would pay. And, with the economy what it is right now, I don't think that would be near a top-dollar value.
sometimes brand name is much much more expensive than the actual property that brand has.
Certainly. I don't think there is really much of any intellectual property of note left within the company, so this theoretically would be a transfer of the name and marks.
As for trying to determine a price, theoretically, you could compare it to similar sales. Certainly the Amiga brand is less memorable name in technology than Atari or Commodore. Both of those turned in low millions, so it is possible Amiga could reach 7 figures, I suppose.
The Atari name and trademark sold in 1998 for $5M (to Hasbro) and again in 2008 for $11M (to Infogrames)
The Commodore name, trademark, c64dtv and other stuff sold for around $25M ($22M Euro to Yeahronimo) back in 2004.
Personally, though, I can't see the Amiga name bringing this type of price. It was never as popular as either of them, and has spent more time without any product available.
Stranger things have happened, though. Apparently
Acer purchased the rights to the Packard Bell name in 2008 for $45.8M. Apparently Packard Bell was still liked in Europe? (News to me...)