If I were you, I’d post a “Wanted to Buy” ad in the classifieds department and state your price and what you’d like. You’d be surprised at how many rifles might be waiting in the wings to get offloaded at a solid price.
You could also build a kit. The superb Kiblers with their long swamped barrels can be had in .50 and are tops. Some here would even say “the cat’s meow” and while I can’t verify this personally as I have never owned a Kibler, some owners claim they even hold the lofty status of “the bee’s knees” and that, my friend, is a superlative endorsement indeed! The total price might be a *bit* out of your pricing range but a call to Jim or Katherine could set you up for success.
Depending on what tools and supplies you have about the house, you might not need to buy a single thing to finish the kit. If you do need tools or supplies, they can be acquired or hunted for at flea markets and so on.
Eventually, you would own a gorgeous rifle made by your own hand that fits your specs nicely. The wonderful people here can help you on the build, too. They’re very simple (the build, not the people). I, for one, am not a builder as I lack the patience and commitment so just buy or commission guns outright.
Lastly, Pedersoli or even Traditions might offer some rifles but typically their barrel are not swamped and don’t balance so well. But, if you’ve a local Cabelas, they sometimes stock the Pedersoli rifles and you can handle them there to get a feel for the way they shoulder and balance. Of course, this would be after the Great Coronavirus Scare of 2020.