Not too long ago, I bought a blue 439 in 98% condition with box and all accessories for around $450. It may be worth much more, but the economy is soft and there are bargains to be had. I'd keep it, but if you're interested in selling it now, you should easily get $450 to $500 for it. If you keep it until the economy gets stronger (don't hold your breath) you could get much more for it. The 439 is a very desirable gun with its alloy frame and second grneration features.
According to the latest version of the Blue Book, a 439 in 100% condition is worth $475. In 98% it's $350. Add $34 for nickel and $25 for adjustable sights. Blue book prices are generally low for my area.