B4R will not be used with Raspberry Pi boards. Only with Arduinos. Technically they are very different.
RPi = Full computer.
Arduino = Micro controller.
Try eBay or adafruit... Arduino boards can vary from 5€ for a UNO clone to +20€ for an original board.
Also there are a few variants like thé duemillenuove, or thé méga...
Projets wise, anything is possible, from drones, self balancing bots to 3D printers and cnc machines
.Thanks for your answers. I have ordered a Adruino Uno . I think it does not have a wifi inside so what must i order to be able to connect the adruino to internet remotely (without a cable i want ) is it possible