I have my 700g male in a 48x24x12 and he's great. I also have 3 hides, foliage, log and water bowl to clutter it up for him. But certainly if you're getting a hatchling, like redsheperd says, that would probably be too big. I'd put a really small BP in a small tub at first. For adults, I'm more concerned with too small rather than too big. You can always clutter up a tank to make the snake feel more secure.
Out of curiosity, what does that exoterra cost? You may be able to get an Animal Plastics T8 for a similar price. You can get a divider for it to make a smaller area until the snake gets bigger.
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