Adruino Swarm - WiFi Communication

I'm developing a model for a robot swarm with the ATMEGA2560 as the main processor. I'd like recommendations of WiFi chips (or boards) that would work well being in up to hundreds of bots at a time. The system will include 1 (or more) central host with a WiFi (master) module to send out tasks to the bots and get data from the bots, and lots of small bots, each of which has its own WiFi (slave) module, to create a DigiMesh network (spreading central commands to peer bots). A range of a few meters should be sufficient, and I'd like to keep the costs low. Also, what protocols should I use for the small bots with will each communicate with their own internal (embedded) modules and the WiFi?
Thank you.