I'd would not pay for Oregon trail or Cast Performance personally, as there are many other casters out there for less, even with gas checks:
http://westernbullet.com/rc44gr.html
http://www.montanabulletworks.com/44_Mag_U99O.html
Just a couple. Both have 300 gr. Gas checked for between $25 and $31 per 100.
Can you get them in larger than standard diameters? Do not get me wrong, cast have their place and it is your choice to pay what you want. After all, the companies that charge $.40/each must be selling some bullets or they would soon be out of business.
The bullets you pointed out are not cheaper than jacketed bullets, basically the same price. That is a problem to me. Why shoot a fast cast, unless you want to push a bullet through a large bodied animal? If that is your goal, then 40 or 50 cents a bullet is in line, but they are more, much more than jacketed bullets. If you want to shoot "plinking" loads or lower velocity hunting bullets, you can find, relatively, cheap cast. If you push these just a little too fast, they will lead your barrel. I do not know about the rest of you, but cleaning lead out of a barrel is not very much fun for me. I do shoot some cheap cast bullets, but I rarely push them above 1000 fps. As time has past, I have moved away from the cheap cast and try to find jacketed bullets for all of my shooting. I can load them down to 1000 fps or up to 4000 fps, depending on application. If you cast your own bullets, then great, I get it. I looked into casting my own, but I do not have a free or cheap source of lead. If I had to buy the equipment, then buy the alloy, throw in the dangers of bullet casting, I just could not justify casting. If you cast your own, then like I said, I get it. I reload and I get a lot enjoyment out of it. It would be hard for some to justify, the expense of rolling your own. As has been said many times, what you do is your business, for me I just do not get paying the same or more for a cast bullet than a jacketed bullet, unless you have a special purpose for it. If I was going to shoot dangerous game with a straight walled case, then a heavy, large diameter, gas checked cast bullet might be the best choice. Other than that I am going to shoot jacketed bullets. I just ordered 1400 jacketed blems that do not cost much more than even cheap cast bullets. For me 1400 bullets is a lot. I ordered 900 .357 and 500 .430 bullets. I do not shoot that much large caliber rounds. I shoot .224 much, much more because .224 is my favorite size bore so I have many rifles that shoot them. They are relatively cheap to shoot too, even with jacketed bullets.
Good Luck and Good Shooting