I think Ellis' asking price isn't completely unfair. Considering it's difficult to messure what the club would be worth for a potential new owner.
Looking at it from a strictly business perspective, I would say any club is not worth owning. Chelsea as an example is loosing two pounds for every pound they make. And they hope to break even somewhere around 2010. Owning a club do however come with certain bonuses as well. Mainly you get a lot of publicity, which can be very positive if that's what you're after. So it's more a question of what the club is worth to potential new owners, rather than finding an exact asking price based on the current financial situation only. Compared to Sunderland I think Villa appears like a bargain, with little or no debt, Premiership club, huge potential, etc etc.
The main reason for Ellis not receiving an offer he can't refuse is that his negotiating position is weakened by the day, rather than asking too much for his shares. His health and age sees to that. Any potential bidder would see it in their best interest not to look for a quick deal, as the chances are that they will get it cheaper tomorrow.
And I also think Ellis is more concerned by selling to the right people, rather than getting the highest price possible. He is, rightly so, concerned with his legacy.