If you are looking at older than 1890, most of the advice above is not what you are looking for, as this limits you to only the first generation Single Action Army. This is not much of a 'limitation', in my opinion, as I prefer the first generation SAA, and prefer pre-1899 SAA's. I don't think you need to necessarily limit yourself to a pre-1890 firearm, because anything produced prior to 1899 is considered an antique, and not a firearm, for BATF purposes. If you want a fiream that is pre-1899, the serial number cut-off is 182,000. If you want a firearm to shoot occasionally that is an antique and can shoot smokeless powder, you would want a firearm in the 165,000 to 182,000 range.
Having said that, if you still want a pre-1890 gun and have $8,000 to spend, the following comes to mind:
First, $8,000 is a really decent budget. You should be able to get something very nice!
Options that come to mind:
I personally, for some reason, like the early SAA's, that were produced for the Civilian market. These are under 22,000, I believe, and contain an Italic barrel address.
Other Civilian options to consider, that are fairly neat, might be a .44-40 Colt Frontier Six Shooter with an acid-etched panel. This is an interesting variation and collectors will spend lots of money for a nice specimen.
A really nice Artillery Model could be had for $8,000, if a military specimen is desired. You could also purchase a Cavalry model for this type of money, but, in the $8,000 range, condition may not be as good as with some of the other options I have suggested.
I really like the early SAA's, and it is something about the 7 1/2 " barrel length with original wood grips that just seems, to me, to be the quintessential Colt. Others on this forum prefer shorter barrel lengths.
In general, blued finishes tend to be more desirable than nickel ones. A bit of wear on a blued finish firearm does not detract from the appearance as much as an identical amount of wear on a nickel gun.
Other advice: BUY the very best quality you can afford for your money. Quality will pay dividends again and again! Also, take your time when it comes to selecting a firearm. Perhaps attend a few antique arms shows and talk to people, see what is out there, etc. Finding this firearm may take months or years. In my experience, when I have money to spend, I do not usually find anything worth buying at any given time. When I am flat broke, usually a lot of nice stuff rears its head.
When you find something nice, look for originality. By going to lots of gun shows and talking with other folks, you might start to get a feel of what is right and what is not. I see you are in Las Vegas and there is a really good antique firearms show out there at least annually.
Another good way to learn is to look at auction house photos and descriptions, such as James Julia and Rock Island.
When you do find something you like, if it is not something you need to buy immediately, such as a 'steal' at an antiques arms show (which usually is not a 'steal' -- if it is too good to be true, it probably is!), you can always post pictures to this forum and several very knowledgeable experts can give an opinion as to what you have and what it is worth and if it is worth the money.
I should mention one other thing: If your goal is a really low serial number, which it does not look like it is, those would be considered a pinch-frame revolver. Those sell upwards of $100,000, usually, so, if in your research, you come across one of these and note the astronomical price asked for it, it is a rare variation that is highly sought after. Other than that, with an $8,000 budget, you have lots of options.
I should state that $8,000 can get you some very nice stuff, but if you want a new, in the box 'look', the pristine stuff goes for well over this amount. But, if you want something very nice, in the 80 % range, for a common civilian firearm, you should have a fair number of options.
One last thing. In my opinion, and this is only an opinion, the Colt SAA market seems fairly high to me. It seems that prices could drop on these in time. However, I could be wrong about this and have been proven wrong in the past. Also, the 'long-term' value of the stuff you and I are interested in is anyone's guess. There is much debate on this, and other, forums as to what will happen to all this stuff, value-wise, when those who hold all this stuff (age 50 +, and often considerably age 50 +) are no longer around. The younger generations tend to like plastic guns (AR-15's, etc.), or are raised in a very anti-firearm culture and fear firearms, antique or otherwise. Thus, in the next 25 years or so, will all this stuff that many on the forum like and collect, hold its value?