You need to do some research on your own here... your original proposal would have given you a slightly fatter viper moray in cramped settings, and you'll likely be unable to find a true viper anyway. Enchelycore nigricans and E. bayeri appear occasionally, and E. lichenosa can be found as well (you can expect to pay $700-$1,200 on those). E. carychroa also appears occasionally, but I wouldn't recommend it - they're incredibly reclusive and you'll likely never see it.
Go with a couple of the miliaris... stunning species, extremely hardy and easy to find.