Check gunbroker completed auctions with the advanced search function.

 

I agree. Completed auctions will give you the best indication of what those guns are going for now. Or you can find the new prices and just take off 20 - 30%, except for the Security Six which is long out of production. I can tell you in round numbers the maximum I'd be willing to pay for them, but I'm cheap, and your local market may be very different from mine.
1. 400
2. 400
3. 300
4. 300
5. 700

 

Keep in mind that values vary by location. The market for GB is the world, not your local market.

 

Newer guns, a lot less than they were bought for originally. The Super RedHawk has held its value.

 

Just last week I bought a stainless Ruger Police Service Six in excellent condition for $475. The Service Six has fixed sights; the Security Six has adjustable sights. That's the only difference. While I was looking for the right Service Six to buy I saw that the price range for stainless Security Six revolvers was solidly in the $500-$700 range, with very few bites on the high end. That's actual selling prices, not inflated asking prices.

I would think that $600 is a pretty good value price. For a 40 year old gun it would have to be pretty minty to be worth $700, IMHO. Others may differ.
-Bob