Ruger old army pistols are about the best BP handgun out there. That being said, they produce marginal power for deer hunting according to some states that have minimum velocities and/or projectile wts for deer hunting.The Old Army may have problems making some of these floors. They are ok at the closer ranges and you should be carefull and keep shots realistic if your state does not have these issues. Accuracy isn't an issue as these guns are typically very accurate.
That price is pretty steep for a used old army. If it were stainless, in the box and pristine, maybe 425. Wasn't too long ago they sold for less than $400 at midway.
Right now they are listing the 5 1/2 blue at 550 and the stainless at 630 without any discounts. You can do better. That being said, prices are being pumped up a bit by the cowboy action crowd and the false perception that there is some "collectability" thing going on with them.
Also, lots of folks do not take good care of the blued ones. They look good on the outside but are rusted junk in the barrel and cylinders. I would look at it very close. If I were going to buy an Old Army, I would go stainless for sure.
I just checked on gunbroker. There are several listed in the 450 range, brand new with buy it now at 449 or so. Here is one link, there are several others. I think you could get a new stainless one for 450 or so pretty easily.
http://www.gunbroker.com/Auction/ViewItem.asp?Item=91859550
Hank