Can someone spec me the cheapest way to get my son online with MarioKart, cable modem

[UOcUK Poopscoop]

Obviously need to go wifi, what would be cheapest method?

We're with Blueyonder.

Just got the cable modem, no routers or anything.

 

[UOcUK Poopscoop]

Thanks for help people. Gotta decide what to do now.