How much would a 4 mile taxi ride cost in Austin at 5am on Saturday?

I want to have an approximation of how much would a taxi ride cost in Austin, at 5-6 am, 4 miles on a Saturday. Do you have any approximation? Please don't tell me it varies, just tell me an approximation. BTW, I would be departing from Greyhound Bus Terminal if that is of any help.|||At least $12, possibly $15.