If you're sure you want an AST, there are breeders out there other than Loggerhead Acres. Not sure when AST's will be hatching, but if you check faunaclassifieds or the classifieds section on Kingsnake every few weeks you're bound to find some.
The native fish with the snapper could work, as long as you don't mind potentially losing some of them. But if you're getting a hatchling, a 180 gallon is honestly way too big. There's no way a young turtle like that can handle water that deep, mine is pushing 4 inches and still can't swim to the top of a 40 gallon tank without a struggle, so I have to give him lots to climb on (and even then it's difficult). So the water level would have to be ridiculously low, and the tank would feel totally empty with just one tiny turtle and only a few inches of water. And like I said, these guys grow slow. If you managed to get your hands on one a bit bigger, you could give it a try, but a 75 gallon would be fine for even a 5 or 6 incher.
There are TONS of other turtles you could keep in that 180 gallon... But from the sound of it you're looking for something a bit more beastly than a plain old stinkpot. You could try a common snapper, those are cheaper, easier to find, and grow quicker (be sure to check you local laws though). If you like CST's but want something a bit more unique, Florida snappers are becoming more popular. They are a very similar subspecies, but they do have a slightly different appearance.
Keep in mind that although common snappers don't get to be 150 pounds, big ones still max out at around 80. So don't think you can get away with a 180 gallon for life.
Most of the other monster turtles start to get a little pricey, even more so than AST's... a Mata Mata housed alone would probably do well in a 180 gallon for live (in the wild they are said to max out at 18 inches but in captivity they rarely get to that size).
There are also the Mexican Musk turtles (Stayrotypus Salvinii & Staurotypus Triporcatus). Salvinii is the smaller of the two, but still gets quite large. I don't know much about these species, same with any of the giant softshells (truthfully softshells sort of freak me out). There are also members of the Podocnemis family, but those are pretty difficult to find and also very expensive (and they get MASSIVE... Not as heavy as AST's but sometimes have a longer/wider shell when full grown).
If none of those ideas intrigue you, if you do a little digging I'm sure you'll be able to find some great ideas all over MFK.