Not that high. The highest .net sale I have heard of is news.net which sold for $150,000 in 2005. So I would guess mid to high xx,xxx. Mp3 technologies might become outdated one day so you have to keep that in mind.
70,000$ range for sure, thats a great name and im sure a company would be willing to buy it. (Kinda like if microsoft wanted ie7.com :S)
I agree. "MP3", is like "Band Aid", or "Cell Phone", people will still refer to it as meaning digital music for some time.