I bought my Ultra II for $800. I just did some searching for the Ultra I. There is very little info about that gun. Maybe a short lived run time. However, I did find one thread, on a forum similar to this, that talked of a person wanting to purchase a used Ultra I. The dealer was asking $650. Before the guy left, the price had been reduced to $550 and then, "make an offer". This was in 2011.
If you really want the gun, I'd offer $400. If there was no bite, walk away. I can't justify more than 50% of new for a model that no longer exists and isn't considered collectible.