Connect arduino to ap for de wi fi

I have a breadboard with sensors with a processor atmega 328p arduino bootloader to read sensors now needed for connecting to a wifi ap to send data to a web service someone can tell me that there are solutions besides the wifi shield because it is very expensive,

I have a s6 xbee wifi 802.11, but I can not put the communicate with the app, find no bookstore, if anyone knows how to

thank you