You want Nordic nRF24L01+ radios. That can be trivially handled by an 8bit micro using SPI, modules with these cost peanuts. However, if you want a PC/phone connectivity you would have to build your own dongle - or reprogram one from a wireless mouse/keyboard. Many use these chips.

Another option is ANT+ - that is very low power but also very low bandwidth (8 byte long messages 4x a second ...) protocol used mostly by fitness gear like training bikes, treadmills and such. Many smartphones have radios that are able to use it. Again something that is easy to make work even with an 8bit micro.

For more advanced stuff there is Zigbee, but that is quite a bit more complex (but still manageable even by an 8bit MCU) and there are some licensing issues which kept it rather obscure.