I want to build a cheap robot programmable in Scratch graphical language, that could be employed during lessons in school. Scratch code is interpreted on a PC, so on the robot there should be only the code that receives specific commands (i.e. drive forward) and transmits sensors' measurements.
I'm looking for a wireless technology that will allow me to exchange information between robot and PC with at least 30Hz rate. It should also allow to work at least 16 robots simultaneously in the same room and have a range of at least 20m.
I did tests with BLuetooth, but sometimes there are connectivity issues, and pairing devices can be a hassle in a classroom. I have also tried WiFi modules, but pinging it showed average time of 19ms, but maximum of more than 500ms, so I'm afraid that it won't be able to control linefollower robot for example.
Can you point me to some other, preferably cheap (under 10$ per module) wireless technologies? Or maybe my worries about WiFi are exaggerated?