Quite a lot.. I saw one user on Reddit who calculated it apparently and he said you can do about 0.65 worth of BTC of trading with 1 BNB token. But the price of BNB fluctuates as well as the price of BTC of course.
But I think it's fair to say that you can do several thousand dollars worth of trading before going through the single BNB token. So one token will get you pretty far actually