By plane
There's a small airport that has a bar open at night. Finding a taxi is next to impossible unless you have someone at hand who can help you find one.
By bus
Taking a bus to Zinder is the best way and, if there are no problems, the trip from Niamey takes 12 to 13 hours. The bus makes frequent stops, about every hour and a half, and a stopover is long enough to buy street food or hit the toilet. SNTV line is the premier one -- they even have a brand new bus, with air-conditioning. It costs 12,500 francs from Niamey, and the return trip is 11,500. "Air" is another good bus line -- they even hand out snacks on the trip. "Rimbo" and the others are sometimes quicker but more dangerous because driving fast in a country with tons of livestock is pretty scary.