There are plenty of cheap bike computers on the market ... The goal is to send crank data to a handlebar-mounted UI via WiFi with a pair of ESP8266 modules. We like the idea of a bicycle area ...

the Lamicall Bike Phone Holder is an excellent option. It has a sturdy handlebar grip and will stay put as you tear up the terrain. The mount also adds a bit of protection to your phone.

GRAND PITSTOP Mobile Holder for Bikes, Motorcycle, Scooter, Bicycles, Claw Grip with Charger Bike Mobile Holder for Maps and GPS Navigation with 360° Rotation Aluminium Handlebar Phone Mount ...