Typical prices are Blue $650 Stainless $850 GCDE $1000+, but you can do better. I've seen blue as low as $550 NIB, but I've also seen idiots asking 1k for a used blue DE.
The Deltas were excellent guns IMHO. With Colt 8-round mags and Wolff XP mag springs mine fed everything like a champ. It was also tight and accurate bone stock. Whatever you do, though, make sure that you have a 100% reputable smith work on it or yours might wind up busted like mine did. Mine is getting fixed by BCP as we speak due to my original stupidity.