Cowboy Action (SASS) shooters drove up the price of fixed sight ROAs because fixed sight revolvers are the only ones allowed in blackpowder competition categories. Yes, blackpowder revolvers are legal in ALL SASS categories, but only revolvers with fixed sights are legal in the restricted blackpowder categories (Frontiersman, Frontier Cartridge, Frontier Cartridge Duelist). Confused? Never mind. It's just the reason fixed sight ROAs are more expensive than ROAs with adjustable sights. Stainless ROAs are also in more demand than blued ROAs, for whatever reason.
The point I want to make is: they aren't being made anymore. If you want a Ruger Old Army and are not interested in SASS competition, your least expensive option is a blued, used, adjustable sight revolver. If you find one in good enough condition for your purposes, and can verify its condition by personal inspection, buy it. At one point I owned 6. Now I'm down to one since I no longer compete.
$100? If you take your wife and grandkids out for a really nice dinner these days, you will spend close to that. I don't let that much money keep me from buying a gun I want.