From the autogarage, leave daily vehicles (19 seats or 9 seats) that cover the 190 km that separate Ayorou of Niamey. The fare is 3000 CFA.
Ayorou is the last major town before the border with Mali, located a few kilometers. Specially in the day market, in the afternoon or the next day, early in the morning, you can find some pirogue that is going to Mali. you can ask the local people for take you into the boat (try to find somebody that help you for the translate) From Ayorou to Gao the price should not exceed 5000 CFA and take few days. If you have time, it will be a nice experience to sahere the trip with the local people Enjoy!
From Arotou to Ansongo and Gao, in Mali, will be a rought journey that take two days by road. The "best" option is a STNV, that every Monday and Thursday a big truck leave from Niamey for try to cross the border. Another option is, if you are lucky, find some truck or public Land Rover that is going to Mali (price is around 8000 CFA to Gao, depend is you travel in the cabin or at the back on top of the merchandise) The vehicle will be crowded and the journey will be hard. Enjoy it!!!
The market day, there are several stalls where you can find meat roasting. The owner will put you in a paper carton with pieces of roasted meat. You can eat on the street or go to some tee stall, who are also small restaurants, and enjoy your meal there. Surely not spend unnoticed among the locals.