I am astounded that even SA revolvers are hard to get. While it is never safe to predict what the insanity of the anti-gun gang might lead to, I venture to say SA revolvers will likely not be banned any time soon.
Still, you won't find any quality SA for under $300 new. But it might be possible to find a used one under that. If you plan to shoot it a lot, it might be best to see if you can find a good used Ruger; they are very rugged and far less likely to have problems than anything else you can find. The drawback is that Rugers, even the Vaquero, are not a true "old West" design (they are better) and some purists don't like them for that reason.